


«3 Q 



f*wnnwnii»iiiuMmi» 



13 



I III 

111! 



EH 1 ! 



lis 






hi 

i i 

I! 



eg 



? \ i 

i t i 



f 



I], 

III 

Si! 



m 



.,OT..M,i,^^;.Wii/-.i'- 




ill 



S&4 Vw«i -'* 



VWWrt\W^tf'JvlVAiV..-V.U: 



TIbe IRurai XTerMKook Series 

Edited by L. H. BAILEY 



SOILS AND FERTILIZERS 



®ijr Rural Eext^ooit Series 

Edited by L. H. BAILEY 
Carleton, The Small Grains. 
B. M. Duggar, Plant Physiology, with 

special reference to Plant Production. 
J. F. Duggar, Southern Field Crops. 
Gay, The Breeds of Live-Stock. 
Gay, The Principles and Practice of 

Judging Live-Stock. 
Goff, The Principles of Plant Culture, 

Revised. 
Harper, Animal Husbandry for Schools. 
Harris and Stewart, The Principles of 

Agronomy. 
Hitchcock, A Text -Book of Grasses. 
Jeffery, Text-Book of Land Drainage. 
Jordan, The Feeding of Animals, Revised. 
Livingston, Field Crop Production. 
Lyon, Soils and Fertilizers. 
Lyon, Fippin and Buckman, Soils — Their 

Properties and Management. 
Mann, Beginnings in Agriculture. 
Montgomery, The Corn Crops. 
Morgan, Field Crops for the Cotton-Belt. 
Mumford, The Breeding of Animals. 
Piper, Forage Plants and their Culture. 
Warren, Elements of Agriculture. 
Warren, Farm Management. 
Wheeler, Manures and Fertilizers. 
White, Principles of Floriculture. 
Widtsoe, Principles of Irrigation Practice. 




Plate I. "The earth is perhaps a stern earth, but it is a kindly 
earth." — Bailey. 



SOILS AND FERTILIZERS 



T. LYTTLETON LYON 

PROFESSOR OF SOIL TECHNOLOGY IN THE NEW YORK 

STATE COLLEGE OF AGRICULTURE AT 

CORNELL UNIVERSITY 



THE MACMILLAN COMPANY 

1919 

All rights reserved 






COPYBIGHT, 1917, 

By THE MACMIUAN COMPANY. 
Set up and electrotyped. Published August, 191^ 



.Nortoooa $regg 

J. S. Cushing Co. — Berwick & Smith Cc 

Norwood, Mass., U.S.A. 



PREFACE 

In many of the high schools and other secondary schools 
into which instruction in agriculture was introduced a few 
years ago there has been such a development of the subject 
that one general text is no longer adequate. In these schools 
some of the more important phases of the subject now re- 
ceive a degree of attention that calls for specialized texts. 
This is particularly true of the secondary agricultural schools 
and the normal schools. It was with the hope of meeting 
this need, and also of contributing to the demands of short 
courses in agriculture and of summer courses for teachers, 
that this book was written. 

The attempt has been made so to present the subject that 
the pupil who has no knowledge of chemistry or other natural 
science will be able to understand it. No chemical symbols 
or formulae have been used. Use has been freely made of a 
limited number of names of chemical substances contained 
in commercial fertilizers which contribute to the nutrition 
of plants. These, however, are terms with which the pupil 
can familiarize himself as readily as with the geographical 
and other names that he has already mastered. 

Following each chapter are field and laboratory exercises, 
designed to illustrate in a concrete manner the teachings of 
the text. There are more of these than any one teacher will 
probably find it expedient to have his class perform, but the 
considerable number and variety of exercises will make it 
possible for any school to afford the necessary facilities for 
performing some of the demonstrations. 



vi PREFACE 

It has not been thought necessary to cite authorities on 
which the statements in the text are based. For these and 
for more complete discussions of most of the matters treated 
in this book, teachers and others who may wish to pursue 
the subject further are referred to the college text on soils 
by Lyon, Fippin and Buckman. 

The author is especially indebted to Dr. H. 0. Buckman 
for much assistance and advice. He has contributed prac- 
tically all of the laboratory exercises. 

Ithaca, N. Y., 
June 1, 1917. 



CONTENTS 

CHAPTER I 

PAGES 

Soil as a Medium for Plant Growth . . . 1-7 

Soil as a mechanical support for plants, § 1 ; Soil 
as a reservoir for water needed by plants, § 2 ; Uses 
of water by plants, § 3 ; Soil as a source of plant-food 
materials, § 4 ; Quantities of plant-food materials in 
the earth's crust, § 5 ; Soil-forming rocks, § G ; Rock- 
forming minerals, § 7 ; Important minerals, § 8. 

Questions on Chapter I ...... 7-8 

Laboratory Exercises ....... 8-10 

Study of soil-forming minerals, I ; Study of soil- 
forming rocks, II ; To show that plants give off 
water, III; Conditions for plant growth, IV; Ef- 
fects of different plant nutrients, V. 

CHAPTER II 

Soil Formation and Transportation . . . 11-16 

Agencies concerned in soil formation and trans- 
portation, § 9 ; Action of heat and cold, § 10 ; Ac- 
tion of frost, § 11 ; Action of water, § 12 ; Action of 
ice, § 13 ; Action of wind, § 14 ; Action of gases, 
§ 15 ; Action of plants and animals, § 16 ; Powdered 
rock is not soil, § 17. 

Questions on Chapter II 16 

Laboratory Exercises ....... 17 

Soil formation and transportation, I. 

CHAPTER III 

Soil Formations 18-28 

Residual soils, § 18 ; Distribution of residual soils, 
§ 19 ; Cumulose soils, § 20 ; Colluvial soils, § 21 ; 

vii 



Vlll CONTENTS 

PAGES 

Alluvial soils, § 22 ; Character and distribution of 
alluvial soils, § 23 ; Marine soils, § 24 ; Distribution 
of marine soils, § 25 ; Lacustrine soils, § 26 ; Glacial 
soils, § 27 ; ^Eolian soils, § 28. 

Questions on Chapter III ....... 28 

Laboratory Exercises ....... 29 

Classification of soils, I ; Use of soil auger in taking 
samples, II. 

CHAPTER IV 

Texttjke and Structure of Soils .... 30-45 
Shape of particles, § 29 ; Space occupied by parti- 
cles, § 30; Mechanical analysis of soils, §31; Me- 
chanical analysis of some typical soils, § 32 ; Soil class, 
§ 33 ; Some properties of the separates, § 34 ; Chemi- 
cal composition of soil separates, § 35 ; Soil structure 
§ 36 ; Relation of structure to pore space, § 37 ; Re- 
lation of structure to tilth, § 38 ; Conditions and 
operations that affect structure, § 39 ; Relation of 
texture to structure, § 40 ; Wetting and drying, § 41 ; 
Freezing and thawing, § 42 ; Effect of organic matter 
on structure, § 43 ; Roots and animals, § 44 ; Tillage 
and structure, § 45 ; Structure as affected by lime, 
§ 46 ; The soil survey, § 47 ; Classification of soils, 
§ 48 ; Information furnished by a soil survey, § 49. 

Questions on Chapter IV . . . . . . . 45 

Laboratory Exercises ....... 46-50 

Examination of soil particles, I; Examination of 
soil separates, II ; Simple mechanical analysis, III ; 
Study of soil class and its determination by examina- 
tion, IV ; Determination of soil class from a mechani- 
cal analysis, V; Soil structure,. VI ; Determination 
of apparent specific gravity of dry sand and clay, 
VII ; Calculation of pore space, VIII ; A study of the 
plow, IX. 

CHAPTER V 

Organic Matter 51-57 

Classes of organic matter, § 50 ; Beneficial effects 
of organic matter, § 51 ; Porosity of organic matter, 



CONTENTS ix 

PAGE8 

§ 52 ; Organic matter and drainage, § 53 ; Organic 
matter and soil color, § 54 ; Organic matter a source 
of plant-food material, § 55 ; Organic matter and 
nitrogen, § 56 ; Organic matter and soil microorgan- 
isms, § 57 ; Organic matter forms acids, § 58 ; In- 
jurious effect of organic matter, § 59 ; Management 
of organic matter in soils, § 60 ; Sources of organic 
matter, § 61. 

Questions on Chapter V . . . . . . . 57 

Laboratory Exercises 58-60 

Examination of soil — organic matter, I ; Exami- 
nation of peat and muck, II ; Estimation of organic 
matter, III ; Extraction of decomposed organic 
matter, IV ; Influence of organic matter on percola- 
tion through soils, V ; Influence of organic matter on 
percentage of moisture held in soil, VI ; Influence of 
organic matter on percentage of moisture held in soil, 
VII. 

CHAPTER VI 

Soil Water . 61-85 

Forms of water in soils, § 62 ; How the three forms 
of water differ, § 63 ; Hygroscopic water, § 64 ; Capil- 
lary water, § 65 ; Capillary water capacity, § 66 ; 
Movement of capillary water, § 67 ; Effect of tex- 
ture on capillary movement, § 68 ; Effect of struc- 
ture on capillary movement, § 69 ; Height of water 
column and capillary movement, § 70 ; Gravitational 
water, § 71 ; The water table, § 72 ; Relations of soil 
water to plants, § 73 ; Ways in which water is useful 
to plants, § 74 ; Water requirements of plants, § 75 ; 
Transpiration by different crops, § 76 ; Effect of 
moisture on transpiration, § 77 ; Effect of humidity, 
wind and temperature of the air, § 78 ; Effect of soil 
fertility on transpiration, § 79 ; Quantity of water 
required to mature a crop, § 80 ; Capillary move- 
ment and plant requirement, § 81 ; Optimum mois- 
ture for plant growth, § 82 ; The control of soil mois- 
ture, §83; Run-off, §84; Percolation, §85;Evap- 



CONTENTS 



oration, § 86 ; Mulches for moisture control, § 87 ; 
The soil mulch, § 88 ; Frequency of stirring, § 89 ; 
Depth of mulch, § 90 ; Effectiveness of mulches, 
§ 91 ; Other devices to prevent evaporation, § 92 ; 
Rolling and subsurface packing, § 93 ; Removal of 
water by drainage, § 94 ; Benefits of drainage, § 95 ; 
Soil air, § 96 ; Soil tilth, § 97 ; Available water dur- 
ing the growing season, § 98 ; Length of growing 
season, § 99 ; Other results of drainage, § 100 ; Open 
ditches, § 101 ; Tile drains, § 102 ; Arrangement of 
drains, § 103 ; Digging ditches and laying tile, § 104. 

Questions on Chapter VI . 

Laboratory Exercises ....... 

Determination of the percentage of water in a soil, 
I ; Capillary movement in different soils, II ; Rate 
of percolation of water through soils, III ; Water- 
holding capacity of soils, IV ; Moisture conservation 
by means of a soil mulch, V ; Loss of water by tran- 
spiration, VI ; Review problems Chapter IV and VI, 
VII; Tile drainage, VIII. 



85 
85-89 



CHAPTER VII 

Plant-Food Materials in Soils .... 90-110 

Variations in content of plant nutrients in different 
soils, § 105 ; The total supply of plant-food materials, 
§ 106; Upward movement of plant-food materials, 
§ 107 ; Plant nutrients compose a small part of the 
soil, § 108; Relation of composition to productive- 
ness, § 109 ; Available and unavailable plant-food 
materials, § 110; Conditions that influence avail- 
ability, § 111; Water-soluble matter in soil, § 112; 
Relation of water-soluble matter to productiveness, 
§ 113; Chemical analysis of soil, § 114; Absorptive 
properties of .soils, § 115 ; Selective absorption, § 116 ; 
The availability of absorbed fertilizers, § 117 ; Other 
forms of available plant-food material in soils, § 118; 
Loss of plant-food material in drainage water, § 119 ; 



CONTENTS xi 



Quantities of plant-food materials in drainage, § 120 ; 
Effect of crop growth on loss of plant nutrients in 
drainage, § 121 ; Effect of fertilizers on loss of plant- 
food materials in drainage, § 122; Drainage water 
from different soils, § 123 ; Absorption of good mate- 
rials by plants, § 124 ; How plants absorb nutrients, 
§ 125 ; How roots aid in solution of soil, § 126 ; Pro- 
duction of carbon dioxide by microorganisms, § 127 ; 
Solvent action of roots in other ways, § 128 ; Differ- 
ence in absorptive power of crops, § 129 ; Substances 
needed by plants and substances merely absorbed, 
§ 130; Quantities of plant-food materials removed 
by crops, § 131 ; Possible exhaustion of mineral 
nutrients, § 132. 

Questions on Chapter VII . . ... . . 110-111 

Laboratory Exercises . . . . . . .111 

Soluble matter of soil, I ; Absorptive power of soil 
for dyes, II ; Selective absorption by soil, III ; Ab- 
sorptive power of the soil for gas, IV. 

CHAPTER VIII 

Acid Soils and Alkali Soils 112-121 

Nature of soil acidity, § 133; Positive acidity, 
§ 134 ; Negative acidity, § 135 ; Ways by which soils 
become sour, § 136 ; Drainage as a cause of acidity, 
§ 137 ; Effect of plant growth on soil acidity, § 138 ; 
Effect of fertilizers on soil acidity, § 139 ; Effect of 
green-manures on acidity, § 140 ; Weeds that flourish 
on sour soils, § 141 ; Crops adapted to sour soils, 
§ 142 ; Crops that are injured by acid soils, § 143 ; 
Litmus paper test for soil acidity, § 144; Litmus 
paper and potassium nitrate, § 145 ; The Truog test, 
§ 146; Alkali soils, § 147; Nature and movements 
of alkali, § 148; Effect of alkali on crops, § 149; 
Tolerance of different plants to alkali, § 150 ; Irriga- 
tion and alkali, § 151 ; Removal of alkali, § 152 ; 
Control of alkali, § 153. 

Questions on Chapter VIII ...... 121-122 



Xll 



CONTENTS 



Laboratory Exercises ........ 

Acid soils in the field, I ; Litmus paper with and 
without potassium nitrate, II ; Litmus paper test, 
III ; Test for soil carbonates, IV ; Ammonia test for 
acidity, V ; Zinc sulfide test for acidity, VI ; Incrusta- 
tion of "alkali" by capillary action, VII. 

CHAPTER IX 

The Germ Life of the Soil 

Microorganisms injurious to crops, § 154 ; Germs 
not directly injurious to crops, § 155 ; Numbers of 
bacteria in soils, § 156 ; Conations affecting bacterial 
growth, § 157 ; Air supply, § 158 ; Moisture, § 159 ; 
Temperature, § 160 ; Organic matter, § 161 ; Soil 
acidity, § 162 ; Bacteria in relation to soil fertility, 
§ 163 ; Action on mineral matter, § 164 ; Decom- 
position of non-nitrogenous organic matter, § 165; 
Decomposition of nitrogenous organic matter, § 166 ; 
Ammonification, § 167; Nitrification, § 168; Effect 
of soil aeration on nitrate formation, § 169 ; Effect of 
temperature on nitrate formation, § 170; Effect of 
sod on nitrate formation, § 171 ; Depths at which 
nitrate formation takes place, § 172 ; Loss of nitrates 
in drainage, § 173 ; Denitrification, § 174 ; Nitrogen 
fixation, § 175 ; Nitrogen fixation through symbiosis 
with higher plants, § 176; Soil inoculation for le- 
gumes, § 177 ; Nitrogen fixation by free-living 
germs, § 178. 

Questions on Chapter IX ....... 

Laboratory Exercises ....... 

Test for nitrates in soil, I ; Test for ammonia in 
soil, II ; Factors affecting nitrate formation, III ; 
Examination of legume nodules, IV ; Examination of 
nodule bacteria, V; Soil inoculation, VI. 

CHAPTER X 

Soil Air and Soil Temperature .... 

Soil air contained largely in non-capillary spaces, 

§ 179 ; There may be too much or too little soil air, 



PAGES 

122-124 



125-140 



40 
140-142 



143-152 



CONTENTS xiii 

PAGES 

§ 180 ; Movement of soil air, § 181 ; Movement of 
water, § 182 ; Diffusion of gases, § 183 ; Composi- 
tion of soil air, § 184 ; Production of carbon dioxide 
in soils, § 185; Conditions that affect the quantity 
of carbon dioxide in soils, § 186 ; Usefulness of air in 
soils, § 187; Oxygen, § 188; Nitrogen, § 189; Car- 
bon dioxide, § 190 ; Control of the volume and move- 
ment of soil air, § 191 ; Soil temperature, § 192 ; 
Sources of soil heat, § 193 ; Relation of soil tempera- 
ture to atmospheric temperature, § 194 ; Factors that 
modify soil temperature, § 195 ; Control of soil tem- 
perature,' § 196. 

Questions on Chapter X ...... 152 

Laboratory Exercises ....... 152-154 

Movement of soil air as measured by texture and 
structure, I ; The presence of carbon dioxide in soil 
air, II ; Production of carbon dioxide by germs, III ; 
Temperature and soil color, IV ; Slope and soil tem- 
perature, V; Drainage and temperature, VI. 



CHAPTER XI 

Nitrogenous Fertilizers 155-168 

Relative quantities of the different forms of nitro- 
gen in soils, § 197 ; Forms in which nitrogen is ab- 
sorbed by plants, § 198 ; Nitrates as plant-food 
materials, § 199; Absorption of ammonia by agri- 
cultural plants, § 200 ; Direct utilization of organic 
nitrogen by crops, § 201 ; Forms of nitrogen in fer- 
tilizers, § 202 ; Nitrate of soda, § 203 ; Crops mark- 
edly benefited, § 204 ; Effect of nitrate of soda on soils, 
§ 205 ; Sulfate of ammonia, § 206 ; Composition of 
sulfate of ammonia, § 207 ; Action when applied to 
soils, § 208; Cyanamid, § 209; Composition of 
cyanamid, § 210; Changes in the soil, § 211; Fer- 
tilizers containing organic nitrogen, § 212; Vege- 
table products, § 213; Animal products, § 214; Fish 
waste, § 215 ; Guano, § 216 ; Effects of nitrogen on 
plant growth, § 217 ; Availability of nitrogenous 



XIV 



CONTENTS 



•fertilizers, §218; Relative values of organic and 
inorganic nitrogenous fertilizers, § 219. 

Questions on Chapter XI . . . 

Laboratory Exercises . . . . . . 

Influence of nitrogen on plant growth, I ; Exami- 
nation and identification of nitrogen fertilizers, II ; 
Comparison of fertilizer effects on plant growth, III. 



168- 



168 
170 



CHAPTER XII 

Phosphoric Acid Fertilizers . . . . * . 171-176 
Bone phosphate, § 220; Mineral phosphates, 
§ 221 ; Basic slag, § 222 ; Acid phosphate, § 223 ; Com- 
position of acid phosphate, § 224 ; Reverted phos- 
phoric acid, § 225 ; Absorption of acid phosphate by 
soil, § 226 ; Relative availability of phosphoric acid 
fertilizers, § 227 ; Rock phosphate versus acid phos- 
phate, § 228 ; Effect of phosphoric acid on plant 
growth, § 229 ; Plants particularly benefited by 
phosphoric acid, § 230. 

Questions on Chapter XII ...... 176-177 

Laboratory Exercises ....... 177-178 

Influence of phosphoric acid on plant growth, I; 
Examination and identification of phosphate fer- 
tilizers, II; Comparison of fertilizer effects on 
plant growth, III. 



CHAPTER XIII 

Potash and Sulfur Fertilizers 

Stassfurt salts, § 231 ; Wood ashes, § 232 ; Insolu- 
ble potash fertilizers, § 233 ; Effects of potash on 
plant growth, § 234 ; Sulfur as a* fertilizer, § 235 ; 
Experiments with sulfur as a fertilizer, § 236 ; 
Quantities of sulfur contained in crops, § 237 ; 
Quantities of sulfur in soils, § 238 ; Quantities of sul- 
fur in drainage water, § 239 ; Sulfur contained in fer- 
tilizers,. § t 240. 



179-185 



CONTENTS 



XV 



Questions on Chapter XIII ...... 

Laboratory Exercises ....... 

Influence of potash on plant growth, I ; Examina- 
tion and identification of potash fertilizers and sulfur, 
II ; Comparison of fertilizer effects on plant growth, 
III. 



185 
185-186 



CHAPTER XIV 



Lime 



Forms of lime, § 241 ; Absorption of lime by soils, 
§ 242 ; Lime requirement of soils, § 243 ; Effect of 
lime on tilth, § 244 ; Effect of lime on bacterial 
action, § 245 ; Liberation of plant-food materials, 
§ 246 ; Effect on plant diseases, § 247 ; The use of 
magnesian limes, § 248 ; Caustic lime versus ground 
limestone, § 249 ; Fineness of grinding limestone, 
§ 250 ; Gypsum or land plaster, § 251. 

Questions on Chapter XIV ...... 

Laboratory Exercises ....... 

A study of the forms of lime, I; Fineness of 
ground limestone, II ; Effect of lime on biological 
action, III; Flocculation by lime, IV; Floccujation 
by lime, V ; Lime and the rotation, VI ; Forms of 
lime to apply, VII. 



187-192 



192 
193-195 



CHAPTER XV 

The Purchase and Mixing of Fertilizers 

Brands of fertilizers, § 252 ; High- and low-grade 
fertilizers, § 253 ; Fertilizer inspection and control, 
§ 254 ; Trade values of fertilizer ingredients, § 255 ; 
Computation of the wholesale value of a fertilizer, 
§ 256 ; Home mixing of fertilizers, § 257 ; Fertilizers 
that should not be mixed, § 258 ; Calculation of a 
fertilizer mixture, § 259 ; How to mix the ingredients, 
§ 260. 



196-205 



Questions on Chapter XV 



205-206 



XVI 



CONTENTS 



Laboratory Exercises ....... 

Fertilizer inspection and control, I ; Laboratory 
mixture of fertilizers, II ; Home mixture of fertilizers, 
III. 

CHAPTER XVI 

The Use of Fertilizers . . . . . . 

Fertilizers for different crops, § 261 ; Small grains, 
§ 262 ; Grass crops, § 263 ; Leguminous crops, § 264 ; 
Root crops, § 265 ; Vegetables, § 266 ; Orchards, 
§ 267 ; Fertilizer mixtures for different crops, 
§ 268 ; Fertilizers for different soils, § 269 ; Calcula- 
tion of results of fertilizer experiments, § 270 ; Fer- 
tilizing the rotation, § 271 ; Methods of applying fer- 
tilizers, § 272 ; The limiting factor, § 273 ; The law 
of diminishing returns, § 274 ; Conditions that influ- 
ence the effect of fertilizers, § 275 ; Response of sandy 
and of clay soils to fertilizers, § 276 ; Cumulative 
need of fertilizers, § 277. 

Questions on Chapter XVI ...... 

Laboratory Exercises ....... 

Fertilization of standard rotations, I; Fertiliza- 
tion of home-farms, II ; Fertilizer practice in the 
community, III ; Fertilizer experimentation, IV. 



PAGES 

206 



207-219 



219 
219-220 



CHAPTER XVII 

Farm Manures . 

Solid and liquid manure, § 278 ; Chemical compo- 
sition of manures, § 279 ; Farm manure an unbal- 
anced fertilizer, § 280 ; Quantities of manure voided 
by animals, § 281 ; Effect of food on composition of 
manure, § 282 ; Commercial evaluation of manures, 
§ 283 ; Agricultural evaluation of manures, § 284 ; 
Deterioration of farm manure, § 285 ; Fermentations 
of manure, § 286 ; Leaching of farm manure, § 287 ; 
Protected manure more effective, § 288 ; Reinforcing 
manure, § 289 ; Methods of handling manure, § 290 ; 
Covered barnyard, § 291 ; Application of manure to 



221-232 



CONTENTS xvii 



land, § 292 ; Place of farm manure in crop rotation, 
§293. 

Questions on Chapter XVII ...... 232 

Laboratory Exercises 233-234 

Study of farm manure, I ; Experiments with farm 
manure, II ; The value of manure produced on the 
home farm, III ; Reinforcement of farm manure, 
IV; Building of a compost pile, V. 

CHAPTER XVIII 

Green-Manures 235-240 

Protective action of green manures, 294 ; Mate- 
rials supplied by green manures, § 295 ; Transfer of 
plant-food materials, § 296 ; Crops used for green- 
manuring, § 297 ; When green-manures may be used, 
§ 298; Handling green-manure crops, § 299 

Questions on Chapter XVIII 240 

Laboratory Exercises ....... 240-241 

Study of green-manure in the field, I; Green- 
manure and the rotation, II. 

CHAPTER XIX 

Crop Rotation 242-247 

Crop rotation and soil productiveness, § 300 ; 
Root systems of different crops, § 301 ; Nutrients re- 
moved from soil by different crops, § 202 ; Some 
crops or crop treatments prepare nutriment for 
other crops, § 303 ; Crops differ in effect on soil 
structure, § 304 ; Certain crops check certain weeds, 
§ 305 ; Plant diseases and insects, § 306 ; Loss of 
plant-food material between crops, § 307 ; Produc- 
tion of toxic substances from plants, § 308 ; Manage- 
ment of a crop rotation, § 309 

Questions on Chapter XIX 248 

Laboratory Exercises .....•• 248 

Crop rotations, I ; Fertilizing the rotation, II. 



LIST OF ILLUSTRATIONS 



Frontispiece 

Rock disintegration by heat and cold . . . facing 6 

Wearing action of water on rock ... . . facing 12 

Plants as soil formers facing 16 

Glacial soil and alluvial soil ..... facing 25 

Stratification of rock and soil .... facing 29 

Auger for taking soil samples ...... 29 

Relative sizes of soil particles 31 

Graphic statement of mechanical analyses of soils ... 33 

Scheme for determining soil class (after Whitney) ... 35 

Ideal arrangement of soil particles 38 

Section showing structure of loam soil in good tilth . . 39 

Plowed land, showing good and poor tilth . . facing 42 

Apparatus for simple mechanical analysis of soil ... 47 
Apparatus for the determination of the apparent specific 

gravity of soil . . . . . . . . .49 

A walking plow and its attachments 50 

Cross sections of furrows turned at different angles . . 56 

Apparatus for the estimation of organic matter in soil . . 58 
Apparatus for estimating rate of percolation and water-holding 

capacity 59 

Soil particles and surrounding films of hygroscopic and capil- 
lary water 63 

Erosion of soil by water and by wind . . . facing 72 

Section of soil with and without a mulch .... 77 

Systems of laying out tile drains ...... 82 

Drain tile outlets facing 83 

Sections of land showing locations of tile drains and water 

tables 84 

Diagrammatic explanation of water control in a humid region 84 

Apparatus for moisture measurement . . . facing 86 
Apparatus for demonstration of effectiveness of mulches in 

conserving soil water ....... 87 

Apparatus for observation of transpiration of water from 

plants 88 



XX 



LIST OF ILLUSTRATIONS 



lime, phosphoric 



facing 
acid and 



PAGE 

92 



Surface soil and subsoil . 
Relative quantities of potash 

nitrogen in a soil ........ 94 

Equipment for making the litmus paper test . . . .123 

Apparatus for making the zinc sulfide test .... 124 

Relative sizes of bacteria and soil particles . . . .128 

Appearance of some soil bacteria (after Lohnis) . . .131 

Diagrammatic representation of the nitrogen cycle . . 139 
Apparatus for estimating the relative rate of air movement 

through soils 153 

Apparatus to demonstrate the presence of carbon dioxide in 

soil air . 153 

Apparatus to demonstrate the formation of carbon dioxide in 

soil 154 

Effect of certain fertilizer constituents on plant growth facing 156 

Extent to which fertilizers are used in the several states . 197 

Tag representative of the kind often used on bags of fertilizer 201 

Plan for fertilizer experiments 212 

Field plat experiments facing 212 

Influence of soil moisture on the effectiveness of fertilizers 

facing 218 

Composition of farm manure ....... 223 

Storage of farm manure facing 226 

Movements of plant-food materials between soil, air and plant 237 

Cover crops which are also green manures . . facing 238 



SOILS AND FERTILIZERS 



SOILS AND FERTILIZERS 

CHAPTER I 

SOIL AS A MEDIUM FOR PLANT GROWTH 

The farmer's interest in the soil is due chiefly to what 
it contributes to plant production. In this respect it per- 
forms several functions : (1) it acts as a mechanical support 
for plants by furnishing a foothold comprising many open- 
ings through which plant roots ramify and hold the plant 
in place ; (2) it serves as a receptacle in which water is 
held in a convenient way for roots to appropriate ; (3) it is 
composed, in part, of substances that dissolve in the water 
which it holds and are absorbed from solution by roots, and 
utilized by plants as food material; (4) its porous nature 
allows air to circulate within it, thus supplying plant roots 
with air. 

These are the contributions that soils make to plant growth. 
Before proceeding with a more detailed study of soil it will 
be desirable to consider briefly the needs of the plant as 
supplied by the soil. 

1. Soil as a mechanical support for plants. — Land plants 
need anchorage, for they must have some permanent supply 
of water and other food material, which is not to be had 
from the atmosphere. The soil serves, at once, as anchor- 
age and food reservoir. One property of soil that adapts 
b 1 



2 SOILS AND FERTILIZERS 

it especially for the growth of roots is its permeable structure, 
which furnishes innumerable channels through which roots 
may ramify ; another property is its compressibility, which 
makes it possible for the roots to grow in thickness by 
forcing together the surrounding particles. The compacting 
thus effected may be noted in a field of mangels or other 
large roots at harvest. The firmness of this anchorage is 
illustrated by the resistance that large trees offer to heavy 
winds. 

2. Soil as a reservoir for water needed by plants. — The 
leaves of land plants thrive without being in contact with 
water, but their roots must have a nearly constant supply. 
This the soil helps to maintain by catching and holding more 
or less of the water that falls as rain. The water thus held 
is in contact with the small roots and root-hairs of plants, 
and may readily be absorbed by them. 

3. Uses of water by plants. — Plants require moisture for 
several reasons : (1) Water acts as a solvent for substances 
that are essential to plant growth, and these substances can 
be absorbed by plants only when they are in solution. 
(2) Water is itself a plant-food material and it either becomes 
a part of the cell without change, or is decomposed and its 
component parts are used in forming new substances. (3) The 
cells, of which plants are composed, are kept filled and the 
plant is more or less firm and erect when its cells are extended 
with water. When not so filled, the plant wilts. (4) Nutri- 
tive substances and substances formed from them in the 
plant tissues are transferred from one part of the plant to 
another, as occasion requires, by water in the plant. (5) The 
evaporation of moisture from leaves (transpiration) causes a 
reduction of temperature in plants, as does evaporation of 
perspiration from animals. 

4. Soil as a source of plant-food materials. — Plants re- 
quire for their growth certain nutrient substances, of which 



SOIL AS A MEDIUM FOR PLANT GROWTH 3 

some are derived from the air and some from water, but 
the larger number must be obtained from soil. They may 
be classified thus : 

Substances obtained from air or water : 

Carbon Hydrogen 

Oxygen Nitrogen 

Substances obtained from soil : 
Nitrogen 

Phosphoric acid [phosphorus] l 
Potash [potassium] 
Lime [calcium] 
Magnesia [magnesium] 
Iron 
Sulfur 

All these substances are essential to the normal devel- 
opment of farm crops. Carbon, oxygen and nitrogen are 
found in air. Hydrogen and oxygen are in water. Plants 
obtain their carbon from the air; their oxygen from 
both air and water ; their hydrogen from water ; their ni- 
trogen, in the case of certain plants only, from the air. The 
other substances are found in all arable soils, from which 
plants obtain them after they have become dissolved in the 
soil water. While arable soils contain all these substances, 
the fact that they must be in solution before plants can use 

1 This list of plant-food materials gives the names commonly used. 
Thus the terms phosphoric acid, potash, and lime are the ones used in con- 
nection with fertilizers. Nitrogen is sometimes spoken of as ammonia by 
fertilizer manufacturers, but the most general term is nitrogen. The words 
in brackets following the unbracketed words indicate other names some- 
times found, but not used in this book. 

All the substances in this list are capable of uniting with certain other 
substances to form various combinations. When present in the soil they are 
not likely to be in the same combinations as when present in plants. When, 
therefore, phosphoric acid in soil or in a plant is spoken of, nothing is implied 
regarding the form in which it exists. 



4 SOILS AND FERTILIZERS 

them sometimes leads to a deficiency in the available 
supply. This is either because they are not present in 
sufficient quantity, or because they are not readily dissolved 
by the liquids with which they come in contact. Many 
things tend to influence the quantity of these substances 
that plants may obtain. Among these are tillage, decaying 
vegetation, drainage and the kind of plant grown. It is 
the nitrogen, phosphoric acid, potash and possibly sulfur 
that are most likely to be deficient in the solution to which 
plants have access, and commercial fertilizers usually con- 
tain one or more of these substances. 

The kind of fertilizer that it will be desirable to apply 
depends, in part, on the so-called availability of eaoh of 
the nutrient substances contained in the soil, availability in 
this case meaning the readiness with which the plant can 
appropriate these food materials. But some plants require 
more of certain of these substances than they do of others. 
Hence the needs of the plant must also be taken into con- 
sideration in deciding what fertilizer to use on a given soil. 

5. Quantities of plant-food materials in the earth's crust. 
: — As all of the food materials that plants draw from soil, 
with the exception of nitrogen, came originally from rocks, 
it is of some interest to know what the proportions of these 
substances are in the entire crust of the earth. As stated 
by Clarke they are present in the following percentages : 

Oxygen 47.17 Potash 3.00 

Iron 4.44 Sulfur ....... 0.11 

Lime 4.79 Phosphoric acid .... 0.25 

Magnesia 3.76 

Nitrogen does not appear in this list because it does not 
occur as a constituent of the rocks forming the earth's crust. 
The nitrogen that soil contains is derived from the atmos- 
phere bjr processes that will be described later. Most of 
the constituents of soil have, however, been formed from 



SOIL AS A MEDIUM FOR PLANT GROWTH 5 

rock, and hence soil may be expected to have a somewhat 
similar composition to that of the earth's crust. 

It will be seen that two of the important nutrients, as far 
as plants are concerned, namely phosphoric acid and sulfur, 
are present in relatively small quantities. Potash, magnesia, 
lime and iron are present in much larger proportions. This 
is somewhat the relation in which we are likely to find them 
in soils, and emphasizes the probable need of phosphoric 
acid and sometimes sulfur for the maximum production of 
crops. Potash, in spite of its greater quantity, is often not 
available in sufficient amount and must be applied as a 
soluble fertilizer. 

Lime, being easily soluble in soil water, has frequently 
been leached out of soils in such quantities that it must 
be replaced. Magnesia is less soluble and hence is rarely 
lacking. 

6. Soil-forming rocks. — As the earth, which was once 
a molten mass, cooled, the crust became solid and this solidi- 
fied material formed igneous rocks, so called to distinguish 
them from rocks that were formed in other ways. Some 
examples of igneous rocks are granite, syenite and basalt. 
Other kinds of rocks, called sedimentary, have been formed 
from material derived from igneous rock by solution and 
sedimentation, and later solidified into rock, often under 
pressure. Limestone, dolomite, shale and sandstone repre- 
sent some rocks of sedimentary origin. The first two are 
quite readily soluble in soil water, having been deposited 
from solution in the process of their formation. Shale 
is a more or less hardened clay. Sandstone, as its name 
implies, consists of sand grains cemented together. 

Metamorphic rocks have been formed by heat, pressure, 
solution and other processes acting on either igneous or sedi- 
mentary rocks. These forces have frequently produced 
rocks quite unlike those originally involved in the process. 



6 SOILS AND FERTILIZERS 

Gneiss, marble and slate are among the rocks so formed. 
Gneiss somewhat resembles granite, from which it is 
formed, but unlike granite has a layered structure, the 
result of the pressure to which it was subjected. Marble 
has been formed from limestone or dolomite by heat and 
pressure, which have caused crystallization. It is not, 
therefore, so readily soluble as limestone. Slate has been 
formed from shale by heat and pressure. 

7. Rock-forming minerals. — Most rocks are not homo- 
geneous, but are made up of a number of different materials. 
An examination will frequently show grains of different 
sizes, colors and hardness. The grains are minerals and 
they differ from each other in their composition as they 
do in their appearance. But each mineral always has a 
more or less well-defined composition, so that when we have 
a certain mineral we know something of the quantity of 
potash or lime or other base that it contains. The quan- 
tity of potash or other plant-food material in a rock will 
depend on the proportion of minerals containing those sub- 
stances that compose the rock. 

8. Important minerals. — There are a few minerals that 
it will be well to mention : (1) because they or their products 
occur in very large quantit} r in soil and influence its physical 
properties ; (2) because of the plant-food material that 
they contain. Quartz and feldspar are examples of the class 
first mentioned. Quartz is found in almost all soils, and 
may form from 85 to 99 per cent of their composition. It 
is particularly prevalent in sandy soils. It usually occurs 
as a large grain, called sand, is hard and insoluble and con- 
tributes no plant-food material. A soil with a great deal 
of quartz is usually a light, easily worked soil. 

On weathering feldspar contributes to soils a mass of 
very finely divided matter known as clay, the smallest of 
the soil particles. It, therefore, forms part of the clay in 




Plate II. Soil Formation. — Heat, cold, and frost have been largely 
instrumental in fracturing the rocks in the upper figure, and in produc- 
ing the rock debris and soil in the lower. Note that vegetation has 
already well started on the slope, 



SOIL AS A MEDIUM FOR PLANT GROWTH 7 

soils and adds to their plasticity, and in addition, this very 
fine material is an absorbent, holding the soluble plant-food 
materials of fertilizers in a form that prevents them from 
leaching from the soil, and yet gives them up to plants rather 
easily. 

As examples of the second class we again have the feld- 
spars as they furnish lime, magnesia and potash; calcite, 
which contains lime ; hematite, which consists largely of 
iron ; dolomite, which contains both lime and magnesia ; 
apatite, which furnishes phosphoric acid and lime, and gyp- 
sum, which is a combination of lime and sulfur. 

These minerals and the plant-food materials contained 
in them may be reviewed in tabular form thus : 



Mineral 


Plant-food Material 


Feldspars 


Potash, lime, magnesia 


Calcite 


Lime 


Dolomite 


Lime, magnesia 


Hematite 


Iron 


Apatite 


Phosphoric acid, lime 


Gypsum 


Sulfur, lime 


Quartz 


Silica (not a plant-food material) 



As these minerals are widely distributed in rocks from 
which soils are formed, they are found in almost all soils, 
and thus it is that all the substances required by plants are 
to be found in most soils. 

QUESTIONS 

1. What are the properties of soil that make it well adapted to 
furnish a mechanical support for plants? 

2. What relation does soil have to the needs of plants for water? 

3. Describe the reasons why plants need water. 

4. Name the elemental substances that plants derive from soil. 

5. What elemental substance do plants obtain from soil that is 
not present in rocks from which soil is formed? 

6. What two substances necessary to plant growth are contained 
in the earth's crust in the smallest quantities ? 



8 SOILS AND FERTILIZERS 

7. In what way were igneous rocks formed ? Sedimentary 
rocks ? Metamorphic rocks ? Name examples of each. 

8. Name a mineral containing potash, a mineral containing lime, 
a mineral containing magnesia, a mineral containing phosphoric acid, 
a mineral containing sulfur, a mineral containing iron. 

LABORATORY EXERCISES 

The following exercises are designed to suggest possible experi- 
ments and demonstrations that may be carried out in connection 
with the various chapters. Some may be performed by the student 
if adequate facilities are at hand, some are only possible as demon- 
strations, while others are field studies and depend on local condi- 
tions. Enough suggestions are made with each chapter to give the 
teacher a range of choice according to his conditions and facilities. 
It is not considered possible or advisable that all the experiments, 
and demonstrations listed be carried out. 

Exercise I. — Study of soil-forming minerals. (The teacher will 
find an elementary text in mineralogy of great aid in this experi- 
ment.) 

Materials. — Small specimens of quartz, potash-feldspar, mica, 
calcite, apatite, gypsum and hematite. Also a piece of a glass, a 
knife, dilute muriatic acid, a hand-lens and flame (gas or alcohol). 

Procedure. — Study the specimens according to the following 
outline, with a view to identifying the minerals unlabeled. Use 
hand lens where possible. 

Hardness. — Determine hardness by the following scale. 

Hardness Mineral 

Scratched by finger na ! l Gypsum\^.. 

Cut by knife Calcite / 

Scratched with difficulty with knife . . Apatite 

Scratches glass Feldspar — Hematite 

Scratches glass very easily Quartz 

Color. — Observe color and luster of the various specimens and 
determine if it is characteristic and useful in identifying the mineral. 

Cleavage and fracture. — Do specimens split easily in certain direc- 
tions or do they fracture ? What effect do these characters have 
upon the appearance (*f the mineral ? 

Form. — Do the specimens seem to have any crystal form that 
is characteristic and useful in identification ? 



SOIL AS A MEDIUM FOR PLANT GROWTH 9 

Action of acid. — What is the result if the specimen is treated 
with a few drops of acid ? Explain. 

Flame. — Hold a small fragment of each mineral in the flame. 
Observe fusibility and change of color. Is the flame given any 
color which is characteristic ? 

Exercise II. — Study of soil-forming rocks. 

Materials. — Small specimens of granite, basalt, shale, slate, 
limestone, sandstone and quartzite. 

Procedure. — Study the color, texture, and structure of each 
sample. Identify the minerals present and from this determine 
the plant-food materials carried by each rock. Be prepared to 
identify unlabeled samples in laboratory and field. 

Exercise III. — To show that plants give off water. 

Materials. — Plant growing in small pot, a tumbler. 

Procedure. — Place a tumbler over a small plant and observe 
the condensation of moisture on the sides. Where does this mois- 
ture come from ? What was its original source ? How do plants 
give off water ? Explain uses of water to the plant. 

Exercise IV. — Conditions for plant growth. 

Materials. — Small flower pots, rich soil, oat seed. 

Procedure. — Fill four small flower pots with a rich garden loam. 
Moisten well and plant with oat seeds. When seedlings are a week 
old, thin to desired number of plants. Grow for a few weeks under 
optimum conditions and then subject them to the following condi- 
tions : 

Pot 1. — Sunshine and optimum water. 

Pot 2. — Sunshine and minimum water. 

Pot 3. — Cold, shade, and optimum water. 

Pot 4. — Dark and optimum water. 

Observe results and explain. More pots with other conditions 
may be tried at the pleasure of the teacher. 

Exercise V. — Effect of the different plant nutrients. 

Materials. — One-gallon flower pots, very poor sandy soil, nitrate 
of soda, acid phosphate, muriate of potash, barley seed. 

Procedure. — Fill five flower pots to withia an inch of their tops 
with poor sandy soil. It is essential to the success of the experiment 
that the soil be poor, and also that it shall be surface soil and con- 



10 SOILS AND FERTILIZERS 

tain some plant food material. Weigh the soil that is placed in each 
pot, mixing with it fertilizer in the following proportions : 

Pot 1, nitrate of soda one part to five thousand parts of soil. 
Pot 2, acid phosphate, one part to five thousand parts of soil. Pot 
3, muriate of potash, one part to ten thousand parts of soil. Pot 4, 
all three of these carriers, each at the rate specified above. Pot 5, 
no fertilizer. Mix the fertilizer and soil thoroughly before placing 
in the pots. Plant a dozen or more barley seeds in each pot. Add 
water in sufficient quantity to make the soil moist but not too wet. 
Place the pots in a place that is moderately warm during the day, 
where they will not freeze at night, and where there is abundant 
light. When seedlings are a week old, thin to ten. Allow plants to 
grow for use in laboratory exercises in Chapters XI, XII and XIII. 
Observe growth in each pot. 



CHAPTER II 
SOIL FORMATION AND TRANSPORTATION 

Side by side are to be seen rock and soil. On the rock 
no vegetation is growing except a few lichens and other 
minute plants. On the soil there is a luxuriant growth of 
multitudinous plants. Soil is derived from rock. Evi- 
dently there must have been a profound change to cause 
such a difference in their relations to plant growth. In 
some regions of the earth there is much rock and little 
soil, while often on the prairie one sees no large rocks, and 
may plow all day and perhaps not strike even a small 
boulder. It may be surmised that in connection with the 
process of soil formation there has been a large transporta- 
tion of material from one place to another. All this was 
brought about by natural agencies, most of which are still 
operating to form more soil and to increase the productive- 
ness of soil already under cultivation. 

The process of soil formation is, however, extremely 
slow, and it must be remembered that thousands and tens 
of thousands of years have elapsed while the operation has 
been in progress. 

9. Agencies concerned in soil formation and transporta- 
tion. — The agencies that have brought about these trans- 
formations may be listed as follows : 



Heat 
Frost 
Wate 


and 
r 


cold 
Plants and animals 


Ice 
Wind 

Gases 








11 





12 SOILS AND FERTILIZERS 

10. Action of heat and cold. — Rocks, as we have seen, 
are mixtures of different minerals. These minerals have 
different rates of expansion when heated. Exposed rock will 
suffer great changes in temperature in twenty-four hours, 
especially if it be located in a region of high altitude and 
cloudless weather. A block of marble one hundred feet 
long will expand one-half inch with a change of 75° Fahren- 
heit, and this is frequently of diurnal occurrence in an arid 
climate. Because the minerals composing rock expand and 
contract at different rates, they tend to tear apart, thus 
producing crevices that may fill with water, and this water 
acts still further to disintegrate the rock. 

11. Action of frost. — One reason that building stones 
are more likely to disintegrate in a cold moist climate than 
in a dry or warm one is that the small pores and cracks on 
their surfaces fill with water, which, when it freezes, exerts 
an enormous pressure. The expansive power of freezing 
water amounts to about 150 tons to a square foot, which is 
equivalent to a column of rock a third of a mile in height. 
The rock surface becomes chipped off by repeated freezing 
and even great masses of rock are detached by the freezing 
of water in larger cracks, as may be seen beneath rock ledges 
in the spring of the year. 

An interesting example of the effect on rock disintegration 
of a cold moist climate as compared with a dry one is found 
in the difficulty that has been experienced in preserving 
the obelisk, now in Central Park, New York, which had pre- 
viously stood for many hundreds of years in the Egyptian 
desert without great damage. It has been found necessary 
to cover the entire surface of the stone with paraffine in 
order to preserve the hieroglyphics carved on its surface. 

12. Action of water. — Water has another effect on rock. 
It is a solvent, weak but universal. It acts on all minerals, dis- 
solving slight quantities of some, considerably more of others. 







Plate III. Water Erosion. — The wearing action of water is slow 
but constant, and is leveling the surface of the earth at the rate of an 
inch in several hundred years. 



SOIL FORMATION AND TRANSPORTATION 13 

It is as a transporting agent that water is most active. 
From the time when raindrops beat down on the surface 
of the soil, while they are gathering into rivulets and the 
rivulets are becoming rivers that discharge into the ocean, 
they are engaged in moving particles of rock debris and 
soil. It is estimated that the United States is being planed 
down at the rate of one inch in seven hundred and sixty 
years. This is rapid enough if it were applied at one point 
to dig the Panama Canal in seventy-three days. 

The carrying power of water has resulted in the formation 
of the rich river valley soils that have been deposited by 
the streams flowing through them. The coastal soils and 
lake soils have also been transported by water. 

13. Action of ice. — In former times a considerable part of 
the northern United States was covered by huge masses of ice, 
known as glaciers. These ice masses were of enormous vol- 
ume and moved slowly in a southerly direction. The great 
thickness of the ice mantles, amounting to several thousand 
feet at some places, caused them to cover hills, valleys and 
mountains, and their enormous weight ground rock surfaces, 
pushed forward heaps of soil and transported huge boulders. 
The southern limit of the glaciers corresponded roughly to 
the lines now marked by the Ohio and Missouri rivers, and 
again extended farther southward along the Pacific coast. 
It met the Atlantic coast at about the present location of 
New York. Changes of climate caused an alternate reces- 
sion and extension of the ice sheets several times, and during 
all this period soil was being formed and worked over by 
the ice and the water that melted from it. When the glacier 
melted, stranded ice masses remained behind. These formed 
lakes in which soil was reworked and shifted, and as the 
lakes finally drained off, the reworked soil was left behind. 
These glacial soils are, as a rule, productive, because of the 
thorough pulverization and mixing they have received. 



14 SOILS AND FERTILIZERS 

14. The action of wind. — That wind has been an active 
factor in the transporation of soil is evident to any one 
who has lived in an arid or semi-arid region, where dust 
storms are not infrequent. In a humid region the move- 
ment of soil by wind is not so patent, but even there, espe- 
cially along the seacoast, there is some movement of this 
kind. There is also an erosive action produced by wind, but 
this has not been very important. However, in arid regions 
the sand -bearing wind has been instrumental in wearing 
away large surfaces of rock, the eroded portions of which 
have helped to form soil. 

The most important result of wind action has been the 
production of loessial soils, which are found in parts of Wis- 
consin, Illinois, Iowa, Missouri, Nebraska and Kansas, 
also in the valley of the Rhine and in parts of China. An- 
other result is the production of adobe soils, which are found 
in mountain sections of western and southwestern United 
States. While these soils do not owe their present location 
entirely to the action of wind, that element has played a 
large part in removing them from other regions and depos- 
iting them where they now are. 

15. Action of gases. — Of the gases that compose the 
normal atmosphere, oxygen and carbon dioxide are instru- 
mental in decomposing rock and soil. They unite chemi- 
cally with some of the substances composing rocks, and 
when the new compound thus formed is more soluble than 
the original substance, the resistance of the rock to water 
is decreased. This is a very constant operation, and as air 
penetrates deeply into soil and into the pores of rock its 
action is widespread. 

16. Action of plants and animals. — Some of the lower 
forms of plants, of which lichens are a notable example, 
are able to live on the bare surfaces of rock, fastening them- 
selves to the small crevices and pores and in the process of 



SOIL FORMATION AND TRANSPORTATION 15 

their growth causing the rock to decay and organic matter 
to accumulate in the crevices. These plants are followed by 
higher vegetation, the roots of which are larger ; when these 
roots extend themselves into cracks in the rock they exert 
a prying action when wind gives the plant a swaying motion. 

After rock becomes sufficiently pulverized to produce 
soil, plants are active agents in decomposing soil particles 
by the solvent action of the acid secreted by their roots 
and formed by their decay. 

Very small plants, included among the microorganisms 
because they are too small to be seen without a microscope, 
are also concerned in rock decay. Their action is exerted 
principally in soil, and is due to the production of acids even 
stronger than that secreted by the roots of higher plants. 

17. Powdered rock is not soil. — We have seen that in 
the process of soil formation the rock is pulverized, but the 
process of weathering to which nature resorts is different 
in its result from merely grinding rock in a crusher or mortar. 
At the same time that the particles are becoming smaller, 
certain chemical changes are going on that produce a ma- 
terial having a different composition from the original rock. 
One result of the transition is the removal of a part or some- 
times all of the more soluble constituents of the rock. The 
percentage loss of some of the constituents of granite and 
of limestone in the process of forming a clay is as follows : 



Table 1. — Percentage Loss 
Granite and Limestone in 


of Plant-Food 
Process of Soil 


Materials in 
Formation 




3TITUENTS 








Percentage 


op Loss 




Granite 


Limestone 


Phosphoric acid 

Potash 

Lime 

Magnesia 


0.00 

83.52 

100.00 

74.70 


68.78 
57.49 
99.83 
99.38 



16 SOILS AND FERTILIZERS 

This table represents merely two cases, and is not meant 
to imply that these losses always occur in just these propor- 
tions whenever rocks of this type are converted into soil. 
It will be noticed that some of the most valuable plant-food 
materials are lost in large quantities. For instance, practi- 
cally all the lime has been lost, as has also a large propor- 
tion of the magnesia and potash. Phosphoric acid shows 
great variation in respect to loss. 

Other changes that occur in weathering include the forma- 
tion of extremely fine particles that give plasticity to soils, 
and that have the property of absorbing certain substances, 
like fertilizers, from solution and holding them in a condition 
in which they do not leach readily from the soil, and yet in 
a form in which roots may make use of them. As these 
particles are very small, we find a relatively large propor- 
tion of them in a clay soil, but a very small proportion in 
a sand. 

Another operation that accompanies soil formation is 
the incorporation of vegetable matter or animal remains — 
together called organic matter — with the soil particles. 
This adds greatly to the crop-producing power of a soil, 
for as the organic matter decays it makes more soluble 
the inorganic constituents. 

QUESTIONS 

1. Name the agencies concerned in soil formation and trans- 
portation. 

2. In what way do heat and cold act to decompose rock ? 

3. What is the action of frost on rock ? 

4. How does water aid in the transportation of soil ? 

5. What part did the great glaciers play in soil formation ? 

6. Has wind been more potent as a soil former or as a trans- 
porter ? 

7. Describe the ways in which roots aid in the decomposition 
of rocks. 

8. Explain the difference between powdered rock and soil. 




Plate IV. Plants as Soil Formers. — Plants are active agents in 
the decomposition of rock. In the upper figure lichens may be seen 
beginning the disintegration, and in the lower, large tree roots are forcing 
themselves into the cracks in the rock. 



SOIL FORMATION AND TRANSPORTATION 17 

LABORATORY EXERCISES 

Exercise I. — Soil formation and transportation. 

This exercise is based on observations in the field and its value 
depends on examples available. Use Chapter II as a basis for the 
field observations. 

If rock outcrops can be found in the neighborhood, a visit to them 
would be worth while. Examples of wind action, heat and cold, 
frost, and plant and animal influences in forming or transporting soil 
should easily be found. The erosive and carrying power of streams 
should also be studied in relation to soil formation. 

An examination of weathered rock of various kinds should be 
made in order to illustrate the chemical phase of soil formation. 
The rusting of iron could be used as an example of the effect of 
gases. The iron of rocks rusts in the same way. This, together 
with the assumption of water and a loss of soluble materials, brings 
about the decay of the rock. Remember, however, that the 
physical and chemical agencies work hand in hand and that these 
agencies are as active upon the soil as upon the original rocks. An 
examination in the spring of fall-plowed land would permit a study 
of the effect of weathering on soil structure. 



CHAPTER III 
SOIL FORMATIONS 

From the preceding description of the processes of soil 
formation, it will be seen that the operation may involve 
the transfer of soil from one place to another, or that it 
may take place in one locality, leaving the resulting soil 
where the parent rocks stood. The latter soils are called 
sedentary, the former transported. These may again be 
subdivided as follows : 

~ , f Residual — formed in place 

Sedentary \ ~ i i 

I Cumulose — plant remains 

Colluvial — gravity deposits 
Alluvial — stream deposits 
Marine — ocean deposits 
Lacustrine — lake deposits 
Glacial — ice deposits 
. ^Eolian — wind deposits 



Transported 



18. Residual soils. — Soils of this formation are geologi- 
cally old, that is, they were formed at an earlier period than 
any of the other arable soils. They always bear more or 
less resemblance in composition to the rocks underlying 
them, although on account of their great age they have lost 
much of the more readily soluble constituents of the original 
rock. This is also of agricultural significance, because 
many of these soluble constituents are of great importance 

18 



SOIL FORMATIONS 



19 



in the growth of plants. The following table shows the 
partial composition of an Arkansas limestone and of the 
clay soil formed from it, also the percentage of each of the 
constituents lost in the process : 



Table 2.- 



Partial Composition of Limestone Rock and Its 
Residual Clay 



Constituents 


Percentage Composition 










Rock 


Soil 


Lost 


Potash 


0.35 


0.96 


66.36 


Lime 


44.79 


3.91 


98.93 


Magnesia 


0.30 


0.26 


89.38 


Iron 


2.35 


1.99 


89.56 


Silica 


4.13 


33.69 


0.00 



It will be seen from the above table that lime, magnesia 
and potash have disappeared in large quantities, as has also 
iron, but that silica has lost little or none of what was orig- 
inally present, and now constitutes by far the larger part 
of the soil. Silica although not of great importance as a 
plant nutrient is, nevertheless, of value in crop production, 
because it contributes to the formation of the absorptive 
compounds before mentioned. 

The great age of residual soils has also led to changes in 
the composition of iron compounds, producing usually those 
of a red or yellow color, these colors being characteristic of 
residual soils. The long period of weathering has frequently 
resulted in wearing down the particles to such a degree of fine- 
ness that heavy soils of the nature of clay, clay loam or silt 
are produced. 

Analyses of two typical- residual soils from Virginia, that 
have been formed from gneiss and limestone respectively, 
are given in the following table : 



20 



SOILS AND FERTILIZERS 



Table 3. — Percentage Composition of Typical Residual 
Soils from Virginia 



Constituents 


Original Rock 


Gneiss 


Limestone 


Phosphoric acid 

Potash 

Lime 


0.47 
1.10 

trace 

0.40 

12.18 

45.31 


0.10 
4.91 
0.51 


Magnesia 

Iron 


1.20 
7.93 


Silica 


57.57 







A striking feature is their low lime content, which is 
characteristic of soils that have been long subjected to 
leaching. Such soils would require applications of lime for 
the profitable production of most crops. The low content 
of lime in the soil derived from limestone illustrates the 
fact that such an origin does not insure a satisfactory supply 
of lime. 

19. Distribution of residual soils. — These soils are 
widely distributed in the United States, being found in four 
great provinces — the Piedmont plateau along the eastern 
slope of the Appalachian mountains, the Appalachian moun- 
tains and plateaus, the limestone valleys and uplands be- 
tween and west of these mountains, and the Great Plains 
west of the Mississippi and Missouri rivers. 

20. Cumulose soils. — Unlike residual soils, cumulose 
soils are of very recent origin. They have been formed by 
the growth of vegetation in and around lakes, ponds and 
marshes, many of which were left by the retreating glaciers. 
As the plants die they become immersed in water, which 
shuts off the supply of air, and thereby arrests decomposi- 
tion. The partly decomposed plant remains accumulate 



SOIL FORMATIONS 



21 



until the surface of the water is reached, when larger plants 
take root, and it is not uncommon to find large forests 
covering soil formed in this way. Cumulose soils, as may 
be expected from their mode of formation, contain a very 
large proportion of organic matter. On the basis of the 
degree of decomposition of the organic matter they have 
been divided into two classes — peat and muck. In peat 
the stem and leaf structure of the original plants may still 
be detected. In muck, however, decomposition has gone 
so far that the organic matter forms a more or less homo- 
geneous mass, and is mixed with a larger proportion of min- 
eral matter than in peat. 

Peat is used extensively as fuel in some European coun- 
tries, but is not of much value for agricultural purposes. 
The degree of decomposition reached by the organic matter 
determines its usefulness for both these purposes. Muck 
cannot profitably be used for fuel, but some muck lands 
are highly prized for market-gardening and other of the 
more intensive agricultural operations. 

The following table shows the composition of some typical 
cumulose soils : 



Table 4. 



Percentage Composition of Some Cumulose 
Soils 



Constituents 


Percentage Composition 


Muck 


Muck 


Marsh Mud 


Mineral matter 

Organic matter 

Nitrogen 

Phosphoric acid 

Potash 


31.60 

68.40 

2.63 

0.20 

0.17 


24.79 

67.63 

2.03 

0.19 

0.15 


80.40 
15.77 

i 

0.15 
0.65 



1 Not determined. 



22 SOILS AND FERTILIZERS 

Many muck soils are underlaid by deposits containing 
lime derived from shells of aquatic organisms that inhabited 
the bodies of water in which the muck was formed. This 
adds materially to the value of the land, as lime is a valuable 
soil amendment, particularly on muck land. It is well to 
keep this in mind when examining muck land. 

The percentage of potash is much lower than in any other 
kind of soils, and a potash fertilizer is usually of great benefit 
to crops planted on muck. 

21. Colluvial soils. — On all steep slopes there is a gradual 
downward creep of soil particles due to the effect of gravity 
assisted by rainfall, freezing and thawing, the movements 
of animals, in fact any agency that starts the particles in 
motion, after which their direction is almost invariably 
downward. This soil formation is not extensive, nor in any 
sense important. Such soils are confined largely to the 
bases of mountains. They are usually shallow and stony. 

22. Alluvial soils. — A stream flowing through its valley 
will erode its bed if very steep and will deposit sediment 
if nearly level, but under most circumstances it both erodes 
and deposits soil. As the upper reaches of a river are usually 
of steeper grade than the lower, it often happens that con- 
siderable material is picked up by the stream near its source, 
and as the current becomes slower farther down, this material 
is deposited. Alluvial soil is, therefore, found most largely 
along rather slowly flowing streams. 

It is estimated that water flowing at the rate of three 
inches a second will carry only fine clay, but if this rate is 
increased to twenty-four inches a second, pebbles the size 
of an egg will be moved along the stream bed. 

It is quite customary for streams flowing through a flat 
region both to erode and deposit soil. Such streams are 
likely to be sinuous in their course, the curves gradually 
becoming more angular as the current erodes the soil from 



SOIL FORMATIONS 23 

the concave bank and deposits it on the convex. Finally 
the curve becomes so great that the stream breaks through 
the banks and straightens its course. In this way a broad 
valley may gradually be covered by sediment deposited by 
the stream. 

Changes in velocity of a stream, as when in flood after 
heavy rains or melting snows, cause a change in its earning 
power. Much material will be picked up by a stream in 
flood that must be deposited as the flood subsides. A 
stream may build up its bed so that the surface of the 
water is higher than is the land at some distance on 
either side. Such is actually the case in the lower Mis- 
sissippi valley. 

23. Character and distribution of alluvial soils. — Allu- 
vial soils may be sands, loams or clay, depending on the veloc- 
ity of the stream and the nature of the eroded material. 
It is likely to be the case that the alluvial deposits along the 
upper stretches of a stream will be sandy, and that the 
material deposited will become finer as the stream proceeds. 
Soils of this formation have no very distinctive composition. 
Naturally this character depends on the nature of the ma- 
terial farther up the stream, and this, of course, varies in 
different parts of the country. Even along any one stream 
there may be a wide diversity of material picked up and 
hence an alluvial soil is likely to be a heterogeneous one. 
The content of organic matter is usually high, as this 
is carried and deposited with the other matter. Alluvial 
soil is generally regarded as rich soil, but there are many 
exceptions. When situated along slowly flowing streams, 
the land is likely to need drainage. 

Alluvial soils are naturally confined to the margins of 
streams, but they are found along small as well as large 
ones, and consequently the aggregate area of alluvial land 
is large. The Mississippi valley and its branches contain 



24 SOILS AND FERTILIZERS 

the largest area of alluvial soil found anywhere in the United 
States. Rivers flowing through the coastal plain are all 
well lined with alluvial soil adjacent to their banks. 

24. Marine soils. — Soils of this formation have been 
made by material carried by rivers and deposited in the 
ocean, whence they afterwards emerged by elevation of the 
sea bottom. They, therefore, resemble alluvial soil that 
has been worked and reworked by sea water. They are 
generally sandy soils, as the solvent action of water and the 
pulverizing force of waves has disposed of most of the min- 
erals except quartz. They are light not only in texture, but 
also in color. They are nearly always deficient in organic 
matter. Their sandy nature fits them particularly well for 
trucking, and it is to that industry that a large area of 
marine soil is devoted. 

25. Distribution of marine soils. — A fringe of land aver- 
aging many miles in width along the Atlantic coast from 
Long Island southward and including all of Florida is com- 
posed of marine soil. This fringe then turns westward 
and extends along the Gulf coast in a wide band as far west 
as the Rio Grande. The alluvial plain of the Mississippi 
river cuts through the belt, but at this point the marine 
soil extends as far north as Tennessee. In the aggregate 
the marine soils constitute a large area of important 
agricultural land producing cotton, corn and other farm 
crops, as well as truck crops for which they are especially 
adapted. 

The following is a statement of the analysis of a typical 
marine soil from the coastal plain in Maryland : 

Table 5. — Percentage Composition of a Typical Marine 

Soil 

Phosphoric acid . . . 0.05 Magnesia 0.35 

Potash. 0.70 Iron 0.91 

Lime 0.41 Silica 92.30 




Plate V. Soil Formation. — The upper figure shows a glacial till 
soil, the lower an alluvial soil. 



SOIL FORMATIONS 25 

A striking peculiarity of this soil is the high percentage 
of silica, due to the fact that quartz is highly resistant 
to the constant working to which the particles have been 
subjected and which has removed much of the phosphoric 
acid, potash, lime and magnesia. Soils of this particular 
type contain little fertility, but respond well to fertilization. 

26. Lacustrine soils. — These soils have been formed 
in the beds of lakes both ancient and comparatively modern. 
The older ones were formed in the glacial lakes, and both 
are soils that have been worked over by water. They 
constitute good agricultural soils and are found from New 
England westward along the Great Lakes, and spread out 
in a wide area in the Red River valley. 

27. Glacial soils. — ■ The tremendous grinding to which 
rocks have been subjected by glacial action has resulted in 
a large proportion of very fine particles, and consequently 
these soils and subsoils are likely to be rather heavy. The 
particles are jagged instead of having the rounded appear- 
ance found in older soils and soils that have been worked 
over by water for longer periods. 

Owing to the fact that this process of soil formation has 
employed mechanical rather than chemical agencies the 
soils resemble the parent rock very closely. Unlike residual 
soils, glacial soils when formed from limestone are generally 
rich in lime. If, on the other hand, glacial soils are formed 
from rocks poor in lime, they have a small lime content. 
The hill soils of southern New York (Volusia series) are 
derived from shales poor in lime and the soils share this 
quality, while certain glacial soils of the Mississippi valley 
(Miami series) that are formed from limestone and sandstone 
are rich in lime. 

In the following table are shown analyses of residual and 
glacial soils from Wisconsin, the original rocks from which 
they were formed having been largely limestone : 



26 



SOILS AND FERTILIZERS 



Table 6. — Percentage Composition of Residual and Glacial 
Clays from Wisconsin 



Constituents 


Residual 


Glacial 


1 


2 


3 


4 


Phosphoric acid .... 


0.02 


0.04 


0.05 


0.13 


Potash 


1.61 


1.61 


2.36 


2.60 


Lime 


0.85 


1.22 


15.65 


11.83 


Magnesia 


0.38 


1.92 


7.80 


7.95 


Iron 


5.52 


11.04 


2.83 


2.53 


Silica 


71.13 


49.13 


40.22 


48.81 



It will be seen that of the substances important for their 
plant-food value phosphoric acid and potash are somewhat 
more abundant in the glacial soils, that lime and magnesia 
are very much more abundant, while the less consequential 
substances are present in large quantity in the residual soil. 
This is because the residual soil has been .subjected to more 
leaching. 

28. ^Eolian soils. — Following the retreat of the glaciers 
there ensued a period of aridity, especially in the southwest 
section of the territory now a part of the United States. Into 
these regions there had been washed a large quantity of 
fine glacial till, and during the dry period this was blown, 
by high westerly winds, into a large area in the Mississippi 
and Missouri valleys, where it is now found. It has been 
given the name of loess and on account of its wide area and 
great fertility it is an important agricultural soil. 

These soils are frequently of great depth, their texture 
is favorable to the maintenance of good tilth and in prairie 
regions their long period in grass, before they were placed 
under cultivation, has given them a good supply of organic 
matter. The following table contains a statement of 
analysis of soils from different sections of the loessal area : 



SOIL FORMATION 27 

Table 7. — Percentage Composition of Loess 



Constituents 



Location of Soil 



Iowa 



Mississippi 



Missouri 



Wyoming 



Phosphoric acid 
Potash . . . 
Lime . . . . 
Magnesia . . 
Iron . . . . 
Silica . . . . 



0.23 


0.13 


2.13 


1.08 


1.59 


8.96 


1.11 


4.56 


3.53 


2.61 


72.68 


60.69 



0.09 
1.83 
1.69 
1.12 
3.25 
74.46 



0.11 

2.68 
5.88 
1.24 
2.52 
67.10 



All of the important plant-food materials, particularly 
lime, are abundant in these soils. They rarely need liming, 
and up to the present time commercial fertilizers have been 
used but little on them. 

Adobe is the name applied to another seolian soil similar 
to loess in its physical qualities, but differing somewhat 
in its mode of formation. It is supposed to be a mixture 
of loess with debris from the mountain slopes and has been 
formed under arid conditions. The soils thus formed are 
extremely fertile when placed under irrigation, which is 
usually necessary for their cultivation, because they are 
found in Colorado, Utah, southern California, Arizona, New 
Mexico and arid portions of Texas. The composition of two 
typical soils is given below : 
Table 8. — Percentage Composition of Two Adobe Soils 



Constituents 

Phosphoric acid . . 

Potash 

Lime 

Magnesia ..... 

Iron ...... 

Silica 



0.29 


0.94 


1.21 


1.71 


2.49 


13.91 


1.28 


2.96 


4.38 


5.12 


66.69 


44.64 



28 SOILS AND FERTILIZERS 

These soils show a remarkably high content of phosphoric 
acid and an abundant supply of the other substances needed 
by plants. 

Sand dunes and volcanic dust are two other forms of 
seolian soils but nowhere are these soils of much agricultural 
importance. 

QUESTIONS 

1. How may soils be divided with respect to the localities in 
which they have been formed ? 

2. What common plant-food materials have been lost in great- 
est quantities by residual soils ? Why are these soils likely to have 
a large proportion of clay ? 

3. In what four regions of the United States are residual soils 
found to be predominant ? 

4. What is the characteristic constituent of cumulose soils ? 
For what agricultural purposes are muck soils largely used ? In 
what important plant nutrient are they likely to be deficient ? 

5. How is the velocity of a stream likely to affect the nature 
of a soil with respect to its proportion of sand and clay ? What 
kinds of streams form little alluvial soil ? 

6. Why are marine soils characteristically sandy ? For what 
agricultural industry are they frequently used ? 

7. Are marine soils usually rich or poor in plant-food materials ? 
Why? 

8. State over what areas in the United States lacustrine soils 
are found. 

9. Why do glacial soils resemble chemically the rocks from which 
they were formed ? What is a characteristic difference between 
residual soil and glacial soil when both are formed from rocks rich 
in plant-food materials? 

10. Describe the mode of formation of the two principal kinds 
of seolian soils in the United States. Are they characteristically 
rich or poor in plant-food materials, and in what one particularly ? 

11. Using any map of the United States as a base (preferably a 
colorless map showing the state boundaries and river courses), draw 
lines tracing roughly the regions occupied by residual, alluvial, marine, 
glacial, and seolian soils. These areas may then be shaded or colored 
differently and a soil map of the United States thus be made. 




Plate VI. Stratification. — The upper figure illustrates stratifica- 
tion of rock, the lower stratification of soil. This shale rock has at one 
time been soil. The soil may sometime be rock. 



SOIL FORMATION 



29 



LABORATORY EXERCISES 

Exercise I. — Classification of soils. 

A study of the various kinds of soils must nec- 
essarily be made in the field. No one locality 
affords examples of all the different kinds of soil 
listed in Chapter III. In some places only one or 
two classes may be available. In any case make 
all possible use of the materials, studying each 
soil as to origin, parent rock, color, depth, sub- 
soil, organic matter, drainage, general fertility 
and crop adaptability. 

Exercise II. — Use of the soil auger in taking 
soil samples. 

Material. — Soil auger and jars or bags for 
samples. 

Procedure. — Explain the construction of a soil 
auger and then proceed with the taking of a sam- 
ple of the first eight inches of soil, removing the 
soil in two portions. Then clean out a hole 
larger than the auger worm to prevent contami- 
nation of later samples and take the second eight 
inches in the way already described. Place sam- 
ples in bags or jars for future reference or exhibi- 
tion. Be sure that the samples are representative 
of the soils to be studied. 

These sample? may be used later in the tests 
for organic matter, acidity, water retention, and 
other demonstrations according to directions in the edge, 
laboratory exercises to be found elsewhere in the 
book. 




Fig. 1. — Au- 
ger for taking soil 
samples. (A) 
handle, (B) joint, 
(C) worm with 
modified cutting 



CHAPTER IV 
TEXTURE AND STRUCTURE OF SOILS 

As a result of the grinding to which rock is subjected in 
the process of soil formation, there are to be found in soils 
particles of all sizes, from gravel and coarse sand down to 
particles so minute that they cannot be seen with the highest 
power microscope, to say nothing of the unassisted eye. 
In all but very sandy soils, particles are generally gathered 
into clusters or granules. Texture is a term used in refer- 
ence to the size of the particles in a soil ; the term struc- 
ture refers to the arrangement of particles into granules. 

29. Shape of particles. — There is no universal shape 
for soil particles. They vary from spherical to angular, 
and are sometimes rather elongated, but the occurrence of 
anything like needle shape is not common. Soils formed 
by erosion and wave action are likely to have rounded 
particles, as are also soils formed from limestone. 

30. Space occupied by particles. — The number of par- 
ticles in a given volume of soil can only be estimated, their 
minute size precludes an actual enumeration. It has been 
estimated that the number of particles in a gram of soil 
of certain different kinds is as follows : 

Early truck 1,955,000,000 

Truck and small fruit 3,955,000,000 

Tobacco 6,786,000,000 

Wheat 10,228,000,000 

Grass and wheat 14,735,000,000 

Limestone 19,638,000,000 

30 



TEXTURE AND STRUCTURE OF SOILS 



31 



If all the particles were spheres, it is estimated that each 
cubic foot of soil would have a surface area on its particles 
amounting to from two to three and one-half acres. 

31. Mechanical analysis of soils. — A separation of the 
particles of a soil into groups, each of which comprises 
particles whose sizes fall within certain definite limits, is 




FINE GRAVEL 
COARSE aAHD 
MEDIUM " 
FlTiE 
T VERY FINE • 
1 SILT 
CLAY 



Fig. 2. — Relative sizes of soil particles in the various grades into which 
a mechanical analysis separates a soil. All are enlarged many times. Par- 
ticles of fine gravel may vary in size from the largest circle to the next largest ; 
coarse sand from the second to the third ; medium sand from the third 
to the fourth, and so on. The dot in the center represents the largest clay 
particles ; the smallest cannot be shown in a figure of this magnification. 



called a mechanical analysis of the soil. The size limit 
of these groups is a purely arbitrary matter, consequently 
it is desirable that a universal system shall be adopted. 
The classification in general use in this country is one pro- 
posed by members of the Bureau of Soils of the United States 
Department of Agriculture. It provides for groups of the 
following sizes : 



32 



SOILS AND FERTILIZERS 









Diameters of Particles 




Millimeters 


Inches 


Fine gravel . 
Coarse sand . 
Medium sand 
Fine sand 
Very fine sand 
Silt .... 
Clay . . . 






2-1 
1-0.5 
0.5-0.25 
0.25-0.10 
0.10-0.05 
0.05-0.005 
less than 0.005 


0.08-0.04 

0.04-0.02 

0.02-0.01 

0.01-0.004 
0.004-0.002 
0.002-0.0002 
less than 0.0002 



32. Mechanical analysis of some typical soils. — When 
soils are analyzed according to the mechanical separation 
just described, there are shown to be great differences 
between some of them, and soils that are adapted to certain 
crops are found to have a somewhat characteristic composi- 
tion. It must be remembered, however, that such dis- 
tinctions are always limited by climate. The following 
table, based on the work of the Bureau of Soils and the 
Minnesota Experiment Station, contains a statement of the 
mechanical analyses of a number of typical soils : 

Table 9. — Meqhanical Analyses of Soils and Subsoils 
Adapted to Certain Crops 





Coarse 

Sand 


Me- 
dium 
Sand 


Fine 
Sand 


Very 
Fine 
Sand 


Silt 


Clay 


Garden truck soil, Norfolk, 














Virginia 


1.42 


28.27 


38.25 


7.51 


21.04 


7.15 


Garden truck soil, Jamaica, 














Long Island .... 


19.06 


24.91 


9.65 


10.08 


17.39 


7.25 


Grass soil, Hagerstown, Md. 


0.08 


0.13 


0.53 


10.94 


23.69 


51.75 


Wheat and grass subsoil, 














Kentucky 


0.00 


0.15 


0.25 


2.34 


39.92 


51.77 


Corn subsoil, Nebraska 


0.00 


0.00 


0.10 


25.83 


57.00 


9.49 


Potato soil, Minnesota . 


0.00 


59.04 


5.60 


28.40 


4.05 


Wheat soil, Minnesota . . 


0.00 


0.00 


6.18 


30.60 


57.00 



TEXTURE AND STRUCTURE OF SOILS 



33 













vSOUli 


MO. 1 










h 

O 

UJ 


90 
£0— 

70 




























i 


60 


UJ 


SO 
40 


? 


ffl 






10 


U 

Mi 






W' 




a 





vm 










wm3k 







FINE C0AR5E1 
GRAVEL SAND 



MEDIUM 
SAND 



FINE 
SAND 



VERY FINE 
SAND 



SILT 



CLAY 



3oii_i iso. a. 



90 
80 
m 
























— 




60 


fO 
40 
no 




zo 








70 

o 



FINE 
GRAVEL 



COARSE. 
S/3ND 



MEDIUM 
S/4ND 



FINE 
SAND 



VERY FINE 
SAND 



5ILT CLAY 



Fig. 3. — Graphic statement of mechanical analyses of two soils. No. 1 
is a very sandy soil, and it will be noted that the bulk of its particles consist 
of medium and fine sand. No. 2 is a heavy clay and its particles belong 
mainly to the silt and clay divisions. 



33. Soil class. — The terms " sandy soil," "loam soil," 
" clay soil " and the like have been in such general use and are 
so convenient that attempts have been made to devise a sys- 
tematic classification on this basis. A soil class is made 



34 



SOILS AND FERTILIZERS 



up of particles of various sizes, but the proportion of the 
large, medium or small particles determines the class to 
which it belongs. The following table published by Whitney 
will show what percentages of soil separates are contained 
in an average sample of each of the soil classes. 

Table 10. — Mechanical Composition of Various Soil Classes 
Based on Averages of Many Analyses 





Fine 
Gravel 


Coarse 

Sand 


Me- 
dium 
Sand 


Fine 
Sand 


Very 
Fine 

Sand 


Silt 


Clay 


Coarse sands . 
Sands 




12 

2 
1 
4 
1 
2 
1 
2 
1 

1 


31 
15 
4 
13 
3 
5 
2 
8 
4 
2 
3 


19 

23 

10 

12 

4 

5 

1 

8 

4 

1 

2 


20 

37 

57 

25 

32 

15 

5 

30 

14 

4 

8 


6 
11 
17 
13 
24 
17 
11 
12 
13 
7 
8 


7 
7 
7 
21 
24 
40 
65 
13 
38 
61 
36 


5 
5 


Fine sands 
Sandy loams . 
Fine sandy loams 
Loam 


5 . 


4 
12 
12 
16 


Silt loams . . 
Sandy clays . 
Clay loams . 
Silty clay loams 
Clays 




15 
27 
26 
25 
42 







There must be a certain amount of variation in the per- 
centages of the separates that go to make up a soil class. 
In order to determine the class to which a soil belongs 
when its mechanical analysis is known, the diagram in Fig. 
4 may be used. If, for instance, a soil contains 40 percent 
of silt and 15 percent of clay, lines are drawn from the point 
marked 40 percent silt and 15 percent clay, the lines being 
parallel to the sides of the right angle formed at 0. It will 
be found that these lines intersect in the space marked 
loam, which is the class to which the soil belongs. If a soil 
has 20 percent silt and 10 percent clay, the intersection of the 
lines drawn from these points falls in the space marked sandy 
loam, and the soil belongs to that class. 



TEXTURE AND STRUCTURE OF SOILS 



35 



cunr 



34. Some properties of the separates. — In addition to 
differences in their size, there are other distinctions that are 
more or less characteristic of these separates. A mechanical 
analysis, therefore, tells us something about several of the 
properties of a soil. 
Clay particles, by 
reason of their mi- 
nute size, tend to 
make a soil plastic 
and may cause it to 
become hard, com- 
pact and cloddy 
when dry. Silt 
does this to a much 
less degree. The 
extent to which a 
soil exhibits these 
properties depends 
on its content of 
clay or silt. Soils 




Fig. 4. — Plan by which the soil class may be 
ascertained from a mechanical analysis. 



much 

clay or silt must not be plowed when wet or they will puddle. 
Both clay and silt serve to increase the water-holding power 
of a soil, and clay especially increases the difficulty of tillage. 

The sand separates have the opposite properties of 
clay, and in the order of their greater size of particles. 
Sandy soils are more easily worked, are not likely to puddle 
or to form clods, and. do not hold a large amount of water, 
but on the contrary have a tendency to become dry. Sandy 
soils are termed " light " soils because they are easy to till; 
clay soils are called " heavy " because they make a heavy 
draft on the plow. 

The absolute specific gravity, or weight of the particles as 
compared with the weight of the volume of water which 



36 



SOILS AND FERTILIZERS 



these particles would displace if they were immersed in it, 
does not necessarily correspond to these terms. Particles of 
greater and less specific gravity are scattered through both 
" light " and " heavy " soils and if we are to find the specific 
gravity of a soil we must have in the sample to be tested 
enough particles to give an average of all in the soil. 

35. Chemical composition of soil separates. — The fact 
that one kind of mineral wears down to a small particle 
more easily than does another indicates that there would be 
a preponderance of resistant minerals, like quartz, among 
the coarse particles and a large proportion of the more 
easily decomposed minerals, like the feldspars, among the 
fine particles. This is actually the case, and it indicates 
a chemical difference in the separates. Analyses of sepa- 
rates made by the Bureau of Soils of the United States De- 
partment of Agriculture bring out these differences, as shown 
by the following table : 

Table 11. — Chemical Composition of Some Soil Separates 





Percentage op 

Phosphoric 

Acid 


Percentage of 
Potash 


Percentage op 
Lime 


Soils 










Sand 


Silt 


Clay 


Sand 


Silt 


Clay 


Sand 


Silt 


Clay 


Crystalline 




















residual . 


.07 


.22 


.70 


1.60 


2.37 


2.86 


.50 


.82 


.94 


Limestone 




















residual . 


.28 


.23 


.37 


1.46 


1.83 


2.62 


12.26 


10.96 


9.92 


Coastal 




















plain . . 


.03 


.10 


.34 


.37 


1.33 


1.62 


.07 


.19 


.55 


Glacial and 




















loessial . 


.15 


.26 


.86 


1.72 


2.30 


3.07 


1.28 


1.30 


2.69 


Arid . . 


.19 


.24 


.45 


3.05 


4.15 


5.06 


4.09 


9.22 


8.03 



It will be noted from this table that, in general, the smaller 
particles are richer in phosphoric acid, potash and lime than 



• TEXTURE AND STRUCTURE OF SOILS 37 

are the larger ones, the only exception being the lime in the 
limestone residual. The arid soils do not show as great 
differences as do the others, because they have not been 
subjected to the same amount of solvent action and tritura- 
tion. 

36. Soil structure. — By soil structure is meant the ar- 
rangement of the particles of which the soil consists. These 
particles may be separated so that each is free to move 
independently of any other, which is usually true of a dry 
coarse sand. Such an arrangement is known as the separate 
grain structure. On the other hand the particles may be 
arranged in small groups or granules, these being so firmly 
combined that the granule acts like a separate particle. 
The latter condition is termed the granular or crumbly 
structure. When applied to loams and clay soils, these 
arrangements of the particles have a relation to the condi- 
tion popularly known as tilth. Good tilth in clays and loams 
implies a granular structure, poor tilth a separate grain 
structure. 

The granular structure is not to be confused with a cloddy 
condition of the soil. In fact clods have the separate grain 
structure, because the soil has been worked when wet until 
the granules are broken down and the particles move easily 
over each other owing to the lubrication of the moisture. 

37. Relation of structure to pore space. — The arrange- 
ment of the soil particles determines to a considerable degree 
the amount of free or pore space within the soil, especially in 
loams and clays. Merely for the purpose of illustrating this 
let us suppose that the soil particles are perfect spheres of 
equal size, which, of course, they are not. There would be two 
arrangements possible, if each sphere were independent of 
every other : (1) in columnar order, in which each particle 
is touched on four places by its neighbors ; (2) oblique 
order, in which each particle is in contact with six of its 



38 



SOILS AND FERTILIZERS 



neighbors. The calculated pore space in the first arrange- 
ment is 47.64 percent. That in the second case is 25.95 
percent. (See Fig. 5.) 

It is not actually the case, however, that soil particles 
are of the same size in any natural soil. Consequently 
small particles fit in between large ones, thus decreasing 
greatly the actual pore space. These three cases, of which 
only the last may occur in nature, illustrate pore space 




Fig. 5. — If all soil particles were spheres they could be arranged as 
shown above, in which case the pore space would vary in volume as ex- 
plained in the text. 

when the separate grain structure obtains, as in a dry sand 
or a puddled loam or clay. 

The granular structure is the one most likely to be found 
in nature, although all of the particles may not be in gran- 
ules. The granules being of irregular form, with many 
angles, there is likely to be a large amount of space between 
them. It would be possible under this arrangement for a 
soil to have a pore space of 72 percent. 

The weight of a given volume of soil, including the pore 
space, as compared with an equal volume of water is termed 
the apparent specific gravity. This it will be seen is not the 
same as the absolute specific gravity because the amount of 
pore space is the important factor in determining the ap- 
parent specific gravitjr. Neither do the terms " light " soil 
and " heavy " soil bear any definite relation to the apparent 
specific gravity. A knowledge of the apparent specific 



TEXTURE AND STRUCTURE OF SOILS 



39 



gravity of a soil is useful because it is an indication of the 
amount of pore space. 

38. Relation of structure to tilth. — The term "tilth" is 
commonly used to denote the condition of a soil with refer- 
ence to plant growth. When the physical condition of a 
soil is favorable to plant growth, the soil is said to be in 
good tilth ; when the physical condition is unfavorable, it is 
said to be in poor tilth. A loam or clay soil to be in good tilth 
must have the greater number of its particles in a granular 
condition. The more sandy a soil the less the necessity for 
a highly granular structure in order that it shall be in good 
tilth. The greater the proportion of clay in a soil, the more 
necessary is the granular structure. One of the great ob- 
jects in soil management is to produce and maintain the 
granular structure. 

39. Conditions and operations that affect structure. — 
So far as the structure of a soil is concerned, something de- 
pends on the inherent quali- 
ties of the soil and something 
on its treatment by the weather 
and by man. These factors 
may be enumerated as follows : 
(1) texture, (2) wetting and 
drying, (3) freezing and thaw- 
ing, (4) addition of organic 
matter, (5) tillage, (6) roots 
and animals, (7) lime. 

40. Relation of texture to 
structure. — A coarse sand 
admits only of the separate 
grain structure. There is not sufficient cohesion to hold 
the particles in granules, and there is no plasticity. With a 
decrease in the size of the particles, there is a greater tend- 
ency to the formation of the granular structure, other con- 




Fig. 6. — Structure of a loam soil 
in good tilth. (A) sand particle, 
(B) pore space, (C) granule com- 
posed of silt and clay particles. 



40 SOILS AND FERTILIZERS 

ditions being equal. This does not mean that a clay soil is 
easier to keep in good tilth than is a loam soil, but under 
favorable conditions the small particles have greater plastic- 
ity and cohesion and hence form granules more readily. 

41. Wetting and drying. — As a soil becomes dry there 
is a contraction of volume in which process lines of cleavage 
or cracks occur and clods are formed. If these clods be 
again wetted and partly dried without working, they will 
separate into smaller clods and finally a granular structure 
will be produced. This is illustrated by the greater ease 
with which clods may be worked down after a rain and 
partial drying, than when they remain perfectly dry. Land 
in need of drainage is usually in poor tilth, while after drain- 
age this condition gradually improves. 

42. Freezing and thawing. — The " heaving " of roots 
during winter is an indication that frost has a disrupting 
action on the solidarity of the soil. Roots are pried out 
because the surface of the soil rises when freezing occurs 
and sinks when melting takes place. Water that is held 
between soil particles freezes when the temperature of the 
surrounding soil falls below the freezing point. As water 
freezes it expands, the effect of which is to force the particles 
farther apart. The pressure applied by the freezing water 
is very unevenly distributed. Around the larger water- 
holding spaces the particles are moved farther than are 
those adjacent to smaller spaces, because the larger the 
body of water the greater the expansion when it freezes. 
The uneven crowding of the particles causes a breaking up 
of the soil into more or less separate masses and as this pro- 
ceeds with repeated freezing and thawing there is a pro- 
nounced formation of granules in a clay or loam soil. 

Fall-plowed land, if left unharrowecl, or if too cloddy to 
work down to a good tilth, will generally be mellow by spring, 
provided there is much freezing weather during the winter. 



TEXTURE AND STRUCTURE OF SOILS 41 

43. Effect of organic matter on structure. — The quantity 
of organic matter in a soil is frequently the deciding factor 
in determining its structure. Partially decomposed organic 
matter has a loose, spongy structure and at the same time 
a plastic quality. The latter causes the soil particles to 
cohere, and the former gives to the organic matter the 
property of swelling when the soil becomes wet and shrink- 
ing when it becomes dry. These changes in volume facilitate 
the formation of granules as previously explained. 

Large areas of land in this country have deteriorated in 
productivity and have become compact and difficult to work 
on account of the gradual loss of organic matter. Naturally 
clay and heavy loam soils have suffered more in this way 
than have lighter soils. Where marked decrease in crop 
returns has occurred during the time that soils have been 
under cultivation, the difficulty can generally be traced to 
loss of organic matter more than to any other factor in plant 
growth. Compact soil, with consequent poor tilth, is one 
of the most common conditions in poor farming regions, 
and is usually associated with a low content of organic 
matter. 

44. Roots and animals. — In some way not very well 
understood roots exert more or less influence on soil struc- 
ture. Shallow, fibrous-rooted plants, among which are 
the grasses, wheat, barley, millet and buckwheat, have the 
most favorable action in granulating soil. More deeply 
rooted, and especially tap-rooted plants, have this property 
to a less extent. In fact, a crop of beets may help to com- 
pact a soil already in bad condition. In establishing a rotation 
it is desirable that some fibrous-rooted plants form one or 
more of the courses. 

Various forms of animal life help to granulate soils. Of 
these, earthworms are the most notable. The soil particles 
that they excrete from the digestive tract may amount to 



42 SOILS AND FERTILIZERS 

several tons in an acre in the course of a year, while their bur- 
rows ramify through the soil in all directions. The move- 
ment of soil particles that results is an appreciable factor 
in changing soil structure. Insects and other burrowing 
creatures affect soil structure in a similar way. 

45. Tillage and structure. — The ordinary operations of 
tillage are designed to improve soil structure, and are effective 
if these operations are conducted at the proper time and in 
the best way. Plowing, which is the most fundamental of all 
tillage operations, may improve soil structure or may injure 
it, depending on the condition of the soil at the time of 
plowing. It is a matter of common knowledge that working 
a soil saturated with water will cause it to puddle, or in 
other words, to assume the separate grain structure. Plowing 
when the soil is very dry may have the same effect, although 
not usually to the same extent. However, when a soil is mod- 
erately moist, plowing aids greatly in effecting a granular 
structure. This it does by the peculiar twisting action that 
the curved moldboard gives to the furrow slice. The soil 
in immediate contact with the plow surface is retarded by 
friction, and the layers above tend to slide over one another 
much as do the leaves of a book when they are bent. The 
soil is thus broken up into masses of aggregates correspond- 
ing to the location of the lines of weakness. If a soil has 
been strongly compacted, so that there are few lines of weak- 
ness, the clods will be large when the soil is plowed. Plow- 
ing helps to improve the tilth of the soil, but it will not over- 
come entirely a bad physical condition. 

46. Structure as affected by lime. — One of the properties 
possessed by lime is that of flocculating clay. This may be 
readily observed by stirring a spoonful of clay in a tumbler 
of water and then adding a quarter of a spoonful of burnt 
lime. It will be noticed that the soil settles much more 
quickly after the lime has been added than before. Sandy 




Plate VII. Tillage. — Good tilth is a response to good soil manage- 
ment. The upper figure is an illustration of poor, the lower of good, tilth. 



TEXTURE AND STRUCTURE OF SOILS 43 

soils are not flocculated to the same extent by lime, but are thus 
affected in proportion to the quantity of clay they possess. 

Of the different forms of lime, quick-lime and water- 
slacked lime are more active in producing a granulated struc- 
ture of soil than is ground limestone, marl or air-slacked 
lime. This is one reason why the burned lime is superior 
to ground limestone for use on heavy clay soils, on which 
there may be a pronounced difference in the effect of the two 
kinds of lime on crop production. Warington reports a 
statement of an English farmer to the effect that by the 
use of large quantities of lime on heavy clay soil he was 
enabled to plow with two horses, while three were necessary 
before applying lime. 

47. The soil survey. — The purpose of a soil survey is to 
classify and map the soils in a given area according to their 
crop relations and their physical properties, and to correlate 
these soils with those in other areas. The soil unit, or what 
may be termed the soil individual, is the type, and on a soil 
map each type is given a different color. Every soil type 
has a certain peculiar and characteristic appearance and 
certain inherent properties that distinguish it from every 
other type. When the type is known some practical infor- 
mation regarding its texture and its amenability to tillage 
and to drainage may be predicted, and something in regard 
to its productiveness and the crops to which it is adapted 
may also often be inferred. 

48. Classification of soils. — In order to distinguish 
between soils, and to give a basis on which to separate them 
into the types to which reference has been made, a form of 
classification has been adopted in this country that takes 
into consideration much of what is known of their history 
and their properties. Thus the first large division into 
which a soil falls is known as the soil province, which is 
based, in a general way, on the process of formation. A 



44 SOILS AND FERTILIZERS 

province may represent residual soil, like the Piedmont 
province, or glacial soil, or marine soil, or soils of other 
processes of formation. 

The next smaller division is the series. A soil series has 
been denned as " a group of soils having the same range in 
color, the same character of subsoil, particularly as regards 
color and structure, broadly the same type of relief (topog- 
raphy) and drainage, and a common or similar origin." 
The last of these properties is due to the fact that soils of 
the same series must fall within the same province. 

The final division is the class, which has been described 
in paragraph 33. A soil class is not limited in its occurrence 
to a soil province, but the same class may be found in all 
provinces. In this respect it differs from a series, any one 
of which occurs only in a single province. 

A soil type represents a soil of a single province, a single 
series and a single class, and represents the features of each. 
The following is an example : 

Province Piedmont 

Series Cecil 

Class Clay 

Type Cecil clay 

49. Information furnished by a soil survey. — The method 
of arriving at the identification of a soil type involves a 
history of the soil, and that may tell something about its 
probable chemical composition, as may be judged from the 
tables of analyses of soils of different formations (§§ 18-28). 
The series we have already found to signify something in 
regard to the working qualities of the soil, as does also the 
class. These distinguishing features are much more marked 
in some types than in others ; in the case of certain types 
considerable definite information is available when the soil 
type is known, while in the case of others less knowledge is 
afforded. Some types always represent a defective soil due 



TEXTURE AND STRUCTURE OF SOILS 45 

perhaps to lack of lime, or poor drainage, or they may 
be characteristically deficient in phosphoric acid or even 
in potash. Again a type is often indicative of the kind 
of crops to which a soil is adapted, but as climate is a 
large factor in determining the success of any crop, conclu- 
sions of this nature are not of universal application. The 
working qualities of a soil may usually be gauged with 
some degree of certainty when the type is known. It is, 
however, as a foundation for a further study of soils that 
the survey is probably of greatest usefulness. 

QUESTIONS 

1. To what does the term " texture " refer when used with refer- 
ence to soils ? 

2. Name the groups into which soils are divided by a mechanical 
analysis. 

3. What characterizes the difference in mechanical composition 
of soils adapted respectively to wheat, corn and potatoes ? 

4. What is meant by class as applied to soils ? 

5. In what class does soil belong that contains 20 percent clay 
and 20 percent silt ? One that contains 40 percent clay and 30 per- 
cent silt ? One that contains 25 percent clay and 35 percent silt ? 

6. How do soils containing a high percentage of clay or silt be- 
have when wet ? How is their water capacity likely to compare 
with that of a soil high in sand ? 

7. How do coarse and fine particles usually differ with respect 
to their content of phosphoric acid, potash and lime ? 

8. What is meant by soil structure ? 

9. Distinguish between separate grain structure and granular 
structure. Which permits of the greater amount of pore space ? 

10. Describe the relation of tilth to structure. 

11. Explain relation of structure to texture. , 

12. Explain relation of structure to wetting and drying of soil. 

13. Explain relation of structure to freezing and thawing of soil. 

14. Explain relation of structure to organic matter. 

15. Explain relation of structure to roots and animals. 

16. How is structure affected by lime ? 

17. How is structure affected by tillage ? 



46 SOILS AND FERTILIZERS 

LABORATORY EXERCISES 

Exercise I. — Examination of soil particles. 

Materials. — Samples of soil, hand lens, high power microscope. 

Procedure. — Examine various sizes of soil particles under the 
hand lens and later under the microscope. Observe shape and 
color. If possible measure size of particles. Try to distinguish 
between silt, clay and sand particles. 

Exercise II. — Examination of soil separates. 

Materials. — The seven separates into which a soil is divided in 
making a mechanical analysis. 

Procedure. — As a soil is made up of the seven grades of parti- 
cles in varying amounts, the characteristics of the grades will 
determine the characteristics of the soil. 

Observe the cohesion and plasticity of each grade. The finer 
grades are usually richer in plant food. Therefore try to imagine 
the physical and chemical properties of different mixtures. Study 
the separates with a view to identification if presented unlabeled. 

Exercise III. — Simple mechanical analysis. 

Materials. — Sandy loam well pulverized, 8 oz. bottle, funnel 
with filter paper, torsion balance, ammonia. (See Fig. 7.) 

Procedure. — Place 50 grams of a dry and well-pulverized sandy 
loam in a bottle of about 8 ounces capacity. Add a few drops of 
ammonia and fill two-thirds full of water. Shake five minutes to 
break up all granules. Then allow sample to stand until the 
various grades of sand have settled to the bottom, after which de- 
cant the silt and clay. Add water and repeat this until the water 
clears as soon as the sands have settled. Then wash the sands 
out into a weighed filter paper held in a funnel. Allow sands to 
drain. Then dry sands and filter paper thoroughly and weigh. 
This weight, less the weight of the filter, will give the weight of the 
sands. Fifty grams, less the weight of the sands, will give the 
weight of the silt and clay. Calculate the percentages of sand and 
of silt and clay respectively in the sample of sandy loam. 

Exercise IV. — Study of soil class and its determination by 
examination. 

Materials. — Hand lens, a number of different soil classes (sand, 
sandy loam, clay loam, loam, silt loam, muck, etc.) labeled for study 
and a set of unknown specimens for identification. 



TEXTURE AND STRUCTURE OF SOILS 



47 



Procedure. — Examine the texture of each of the labeled soils 
both under the hand lens and by the feel. Observe the color Eftid 
estimate the amounts of organic matter by the darkness of the color. 
Be able to identify samples if unlabeled. 

Observe the plasticity and cohesion of each soil when enough 
water has been added to develop maximum plasticity. Make small 
marbles of sand, clay and muck respectively when each is at its 
maximum plasticity. Dry and observe relative cohesion and 
plasticity. Be able to state the relation of texture, moisture and or- 





SILT 
CLAY 



•5ANDS 




APPARATUS FOR FILTERING 5ANDS 



Fig. 7. 



Apparatus for a simple mechanical analysis of soil, 
bottle, funnel, filter, beaker and stand. 



Shaker 



ganic matter to cohesion and plasticity. What is the practical im- 
portance of texture and class ? 

Obtain set of unlabeled samples for identification of class. If 
possible, pupils should also identify samples in the field. As mois- 
ture variations and tillage operations often make great differences 
in the general appearance of a soil, skill in quickly and accurately 
determining the class of any soil in the field is a valuable asset in 
all agricultural work. 

Exercise V. — Determination of soil class from a mechanical 
analysis. 

Materials. — Figure on page 35. 



48 



SOILS AND FERTILIZERS 



Procedure. — By the use of the chart determine the class of the 
following soils and describe their probable characteristics. 



Soil 


Fine 
Gravel 


Coarse 
Sand 


Medium 
Sand 


Fine 
Sand 


Very 
Fine 
Sand 


Silt 


Clay 


1 


1 


5 


6 


5 


3 


70 


10 


2 


2 


3 


10 


18 


12 


45 


10 


3 


1 


2 


14 


18 


25 


30 


10 


4 


2 


3 


25 


14 


16 


30 


10 


5 


3 


7 


25 


30 


20 


10 


5 


6 


2 


3 


12 


19 


24 


10 


30 


7 


1 


4 


9 


11 


10 


40 


25 


8 


2 


2 


3 


4 


4 


60 


25 


9 


1 


2 


7 


6 


4 


20 


60 


10 


2 


1 


3 


2 


2 


50 


40 



Be ready to explain the practical value of a mechanical analysis. 

Exercise VI. — Soil structure. 

Materials. — Puddled and granular soils. 

Procedure. — Examine under hand lens a granular and a puddled 
soil. Describe each and make drawings. Discuss each as to prob- 
able relation to air and water movement, penetration of plant roots, 
ease of making seed bed, etc. Be ready to suggest practicable reme- 
dies for poor structure. 

Exercise VII. — Determination of apparent specific gravity of 
a dry sand and clay. (See Fig. 8.) 

Materials. — Torsion balance, dry soils and a 100 c.c. graduated 
cylinder. 

Procedure. — Apparent specific gravity is the weight of dry soil 
compared to the weight of the same volume of water. 

Weigh the 100 c.c. graduate in grams, then fill to the 100 c.c. 
mark with loose sand. Weigh and calculate the weight of the sand 
in grams. The weight of the sand divided by 100 (the weight of 
100 c.c. of water in grams) will give the apparent specific gravity of 
the loose sand. Now compact the sand as much as possible by 
jarring and read volume. Divide the weight of the sand by this 
volume to obtain the apparent specific gravity of the sand compact. 



TEXTURE AND STRUCTURE OF SOILS 



49 



Determine in the same way the apparent specific gravity of the 
clay when loose and when compact. 

Compare the figures from each soil and explain the reasons for 
the differences observed. 

Calculate the weight per cubic foot and acre foot of the sand and 
clay when loose and when compact. 




Fig. 8. — Equipment for the determination of the apparent specific 
gravity of soil, consisting of a balance, a set of weights and a 100 c.c. gradu- 
ated cylinder. 

Exercise VIII. — Calculation of pore space. 

Materials. — Data from Exercise VII. 

Procedure. — Using 2.7 as the absolute specific gravity of soils 
and the data from the preceding exercise, calculate the pore space 
on loose and compact clay and sand respectively by means of the 
following formula. 

% pore space = 100 - |~ ^P S P- gr. x ^1 ' 
Labs. sp. gr. 1 J 

Be ready to explain the reasons and significance of the results 
obtained. 

1 Ap. sp. gr. means apparent specific gravity. Abs. sp. gr. means absolute 
specific gravity. 



50 



SOILS AND FERTILIZERS 



Exercise IX. — A study of the plow. 

Material. — Garden plow and team. 

Procedure. — Study the plow by following the diagram in Fig. 9. 
Locate the mold board, point, share, landside, shin, heel beam, 
coulter and clevis. 

Adjust the plow to various widths and depths of furrow slice, 
trying out each adjustment by throwing several furrows. Be sure 
that with each adjustment the plow operates properly. 




fi—t^j^. 



Fig. 9. — A walking plow and its attachments, (a) clevis, (b) beam clevis, 
(c) bridle, (d) beam, (e) mold board, (/) depth wheel, (g) rolling coulter, 
(h) jointer, (i) standard, (j) share point, shin above, (k) landside. 



Study the inversion of the furrow slice and be ready to explain 
how and why a plow is a good pulverizing agent. The pupils should 
hold the plow as much as possible in the various tests. 

If a sod plow is available, a study of this form would be of value, 
comparing it with the garden plow above. A comparison of a walk- 
ing plow with a sulky plow would also be worth while. 

A visit to an implement dealer for the purpose of looking over 
the various makes of plows might be a profitable exercise. The 
manufacturer's and the dealer's viewpoint is as valuable as that 
of the farmer. 



CHAPTER V 
ORGANIC MATTER 

A very important constituent of soil is the more or less 
decomposed organic matter that has become incorporated 
with it. Organic matter is found in larger quantity in sur- 
face-soil than in subsoil because it comes largely from vege- 
table matter that has fallen on the surface and there decayed, 
or that has been plowed under. Animal remains and lower 
forms of plant life also contribute to the supply. The roots 
of dead plants are one source of organic matter, and as these 
generally penetrate into the subsoil they deposit a limited 
quantity of organic matter in that part of the soil. 

50. Classes of organic matter. — Organic matter that 
is incorporated with soil gradually decomposes, forming 
substances that are very different in their properties from 
the original material. The process may be roughly divided 
according to the degree of decomposition into three classes, 
viz : (1) undecomposed matter, (2) partially decomposed 
matter, (3) final products. The substances representing 
each of the stages in the process have different properties 
and differ in their effect on soil. 

Undecomposed organic matter is of use in making less 
compact a heavy soil ; on the other hand, it may make too 
loose a naturally light soil and may cause it to dry out to 
such an extent that its productiveness will be curtailed. 
For instance, a stand of oat stubble or of corn stalks that 
would be of much benefit to a heavy soil in a humid region 
might injure seriously a light soil in a semi-arid region. 

51 



52 SOILS AND FERTILIZERS 

Partially decomposed organic matter is of benefit to soils 
in a number of ways and it may also be injurious. These 
properties will be discussed later. The term " humus" 
has been somewhat loosely used with reference to the sub- 
stances of this class. It will not be used in this book. 
Organic substances represent a. wide range of intermediate 
products of decomposition. They profoundly affect the 
properties of soils and are always present in arable soils. 

Final products of decomposition of organic matter are 
water and gases. The latter may unite with some of the 
inorganic matter of the soil to form purely inorganic sub- 
stances, and these are as a rule readily available to plants. 
They differ from the substances of the other two classes in 
that none of them is injurious to crop production. 

51. Beneficial effects of organic matter. — There are 
many ways in which organic matter may benefit soils, either 
directly or indirectly. Soils differ somewhat in the effect 
that organic matter may have on some of their properties. 
An example of this has been cited in the effect of organic 
matter on a heavy soil in a humid region as compared with 
its results in a light soil in a semi-arid region. Another 
example is to be found in the results that follow the plowing 
under of green-manures. In some soils and under certain 
conditions this may be temporarily injurious, although it 
is usually a very beneficial practice. 

An enumeration of the beneficial effects of organic matter 
in soil is necessarily open to criticism on account of the dif- 
ferent responses of different soils, but with some modifications 
the following will hold. 

(1) It increases the tendency towards the formation of 
granular structure. 

(2) On account of the porous nature of organic matter 
the pore space of the soil is increased and aeration improved. 

(3) It increases the water-holding capacity of soils. 



ORGANIC MATTER 53 

(4) It improves drainage by reason of the properties 
stated under (1) and (2). 

(5) It increases the extent of root growth for the same rea- 
sons. 

(6) By making the soil darker, it facilitates heat absorp- 
tion. 

(7) It is a source of plant-food material. 

(8) It furnishes energy for the growth of bacteria. 

(9) Its decomposition produces carbonic acid gas and 
other acids that help to render plant-food materials soluble. 

52. Porosity of organic matter. — The way in which or- 
ganic matter promotes a granular structure in soils has 
already been described, as has also the relation of soil struc- 
ture to tilth. In addition to this effect on soils, organic 
matter also serves to make soil more porous by reason of 
its own porosity. It may be compared to a sponge in its 
ability to hold air or water. A peat soil, for instance, will 
hold more water than its own weight of dry matter. Or- 
ganic matter extracted from a peat soil was found to carry 
twelve times its own weight of water. It may readily be 
seen that the porous nature of this organic matter may 
greatly increase the water-holding capacity of a soil. At 
the same time it may increase the capacity of the soil for air. 

53. Organic matter and drainage. — By reason of the 
greater porosity due to the presence of organic matter, the 
movement of water through soils is facilitated and thus the 
soil is better drained. The advantages of good drainage 
will be discussed more fully later, but an important one 
of these is a greater growth of roots, which increases their 
opportunity for securing food and thus increases the size of 
crop. 

54. Organic matter and soil color. — Partly decomposed 
organic matter generally gives a dark color to a soil. A 
dark soil absorbs heat more readily than does a light-colored 



54 SOILS AND FERTILIZERS 

one, and as warmth is an important factor in plant growth, 
especially in the spring, a dark soil usually has an advantage 
over a light-colored one. 

55. Organic matter a carrier of plant-food material. — 
In its relation to the supply of plant-food material, organic 
matter is the storehouse in which nitrogen is held in a form 
in which it cannot be leached from the soil in large amounts 
and yet from which it gradually becomes available to plants. 
Certain inorganic plant nutrients are likewise held in such 
condition that they readily become useful to plants. In the 
process of rotting, combinations are formed between organic 
matter and certain inorganic plant nutrients, removing the 
latter from the very insoluble minerals of the soil. On 
further decomposition the inorganic substances are left in a 
form readily usable by plants. 

56. Organic matter and nitrogen. — The relation of 
organic matter to the nitrogen supply is of particular inter- 
est because it is as organic matter that practically the entire 
supply of nitrogen enters the soil. All soil nitrogen has been 
secured from the air and the process is still going on. This 
is done largely by the lower .forms of plant life known as 
bacteria, fungi and molds. These organisms living in the 
soil, or in the roots of higher plants, feed on the non-nitrog- 
enous organic matter of the soil and plants, and upon the 
nitrogen of the atmosphere that passes into the pores of the 
soil. The non-nitrogenous organic matter and the atmos- 
pheric nitrogen are thus combined to form the tissues of 
these lower plants, which soon die and finally add to the 
soil the nitrogen they have accumulated. 

57. Organic matter and soil microorganisms. — We have 
just seen how the nitrogen-fixing organisms use non-nitrog- 
enous organic matter in their growth. They use it as a 
source of energy, as do animals. Many other forms of lower 
plant life use organic matter, both nitrogenous and non- 



ORGANIC MATTER 55 

nitrogenous. As the growth of these organisms is very 
necessary in making the various sorts of plant nutrients 
available, the supply of organic matter for this purpose is 
of great importance. 

58. Organic matter forms acids. — Finally, organic matter 
in its very last stages of decomposition continues to serve 
the plant by producing carbonic acid gas, which, dissolved 
in soil water, is an excellent solvent for many mineral sub- 
stances needed by plants. It is estimated that in an acre 
of soil sixteen inches deep, sixty-eight pounds of carbon 
dioxide are produced annually from the decomposition of 
organic matter when present in ordinary quantity. There 
are also other organic acids formed by the rotting of or- 
ganic matter that serve to dissolve the inorganic matter of 
soils. The combinations of these organic acids with min- 
eral substances form readily available plant-food materials. 
Another final product of nitrogenous organic matter is 
nitrate, Which is the most available form of nitrogen for 
many plants. 

59. Injurious effect of organic matter. — The injury that 
organic matter may cause is probably not of very frequent 
occurrence and is unimportant as compared with its benefi- 
cial action. Two effects have been noted : 

(1) Undecomposed organic matter may cause a soil to 
dry out quickly by preventing it from settling sufficiently 
to establish water connection with the subsoil and by leav- 
ing large air spaces that allow a rapid movement of air 
through them which dries out the soil. 

(2) Partially decomposed organic matter may form prod- 
ucts that are poisonous to some agricultural plants or that 
interfere with the operations of those microorganisms that 
are beneficial to plant growth. 

60. Management of scil with respect to organic matter. — 
The first step in the control of organic matter in soil is to 



56 



SOILS AND FERTILIZERS 



bring about decomposition, which operation is performed 
by bacteria, fungi and molds. It has already been pointed 
out that unrotted organic matter has very little useful- 



(WBfftj 







Fig. 10. — The upper figure represents a furrow slice laid too flat for the 
most rapid decay of organic matter when present in large quantity. The 
lower illustration shows a better furrow angle. 

ness and may be injurious. The conditions that favor the 
rapid and desirable rotting of organic matter are the fol- 
lowing : 

(1) An amount of moisture that will not fill all of the 
pore spaces, but that will provide water required by 
the organisms that decompose the organic matter. The 
soil moisture content most favorable for plant growth is 
about the same as that most favorable for rotting organic 
matter. 

(2) The soil should be loose enough to allow air to pene- 
trate readily, but not so loose as to leave large air spaces. 
Air is necessary to the activity of those organisms that pro- 
duce a desirable kind of decomposition. A compact soil, 
or a very wet soil delays the rotting process and favors the 
growth of organisms that form products poisonous to agri- 
cultural plants. 



ORGANIC MATTER 57 

(3) The soil should not lack lime, as the presence of lime 
in a readily soluble form favors the development of many 
forms of life that decompose organic matter, and it also 
prevents the poisonous action of certain substances pro- 
duced in the process. 

61. Sources of organic matter. — In addition to the 
natural supply of organic matter referred to in the first part 
of this chapter, there are other sources from which the 
farmer may obtain a supply by outright purchase or by 
means of their production on the farm. Among these are 
farm manure, grass and clover sod, green-manures, peat and 
muck, crop residues, like straw, cornstalks and leaves, dead 
animals, certain commercial products, like cottonseed meal 
and dried blood, and finally weeds, which are sometimes used 
for that purpose in orchards. 

These various materials and their use in contributing to 
the supply of organic matter in soils will be discussed later 
under the respective heads (1) farm manure, (2) green- 
manures and (3) commercial fertilizers. 

QUESTIONS 

1. Into what three classes may the organic matter of the soil be 
divided ? 

2. What is the effect of organic matter on the water-holding 
capacity of soil ? 

3. What is the effect of organic matter on drainage ? 

4. How does organic matter contribute to the availability of 
plant nutrients in soils ? 

5. In what general way does organic matter affect the growth of 
bacteria in soils ? 

6. How do the final products in the decomposition of organic 
matter increase the availability of plant-food materials in soil ? 

7. In what two ways may organic matter be injurious to soils ? 

8. What are the soil conditions that favor a rapid and desirable 
decomposition of organic matter ? 

9. Name the sources of organic matter that may serve to increase 
the supply in soils. 



58 



SOILS AND FERTILIZERS 



LABORATORY EXERCISES 

Exercise I. — Examination of soil for organic matter. 
Materials. — Samples of clay soils respectively low and high 
in organic matter, hand lens, flame. 

Procedure. — Examine a soil rich in organic matter under the 
hand lens. Observe character of the organic matter, its color and 
its effect on structure. Compare the structure of the soils high and 
low in organic matter. What effect does the organic matter ap- 
pear to have upon granulation ? How should the organic matter 
influence the ease of preparing a seed bed? How does organic matter 
influence percolation of water through a soil ? How does it affect its 
water capacity ? 

Place a small portion of the soil rich in organic matter in the 
flame. Observe and explain the results. 

Exercise II. — Examination of peat and muck. 
Materials. — Samples of peat and muck, hand lens, flame. 

Procedure. — Examine samples 
under lens and describe and make 
drawings. What is the origin of 
the materials, their structure, com- 
position and degree of decay ? 
What is the value of peat and 
muck ? 

Place a small portion of each in 
the flame. Observe and explain 
results. What is shown regarding 
the composition of peat and muck ? 
Exercise III. — Estimation of 
organic matter. 

Materials. — Soil samples, cru- 
cible, stirring wire, flame, tripod, 
clay triangle, balance. 

Procedure. — Place a five-gram 
sample of dry soil in a weighed 
crucible. Ignite with frequent 
stirrings at a low red heat over a flame until original dark color has 
disappeared. Cool and weigh. The loss has been largely organic 
matter. Calculate the percentage based on the original sample. 
Find in this way the percentage of organic matter present in several 
different soils. 




Fig. 11. — Apparatus for the esti- 
mation of organic matter in soil. 
(A) crucible, (B) clay covered tri- 
angle, (C; tripod, (D) Bunsen burner. 



ORGANIC MATTER 



59 



Exercise IV. — Extraction of partly decomposed organic matter. 

Materials. — Muck, dilute hydrochloric acid, ammonia, hydrate 
of lime, filter paper and funnel. 

Procedure. — Place about a gram of moist muck on a filter paper 
in a funnel. Treat the muck with a few drops of dilute hydrochloric 
acid. Wash out the acid with 50 c.c. of distilled water. Discard 
this percolation. Now treat the soil with ammonia. After allow- 
ing it to stand a few minutes wash with distilled water and catch 
percolate. 

The percolate should be black, showing the presence of partly de- 
composed organic matter. This is the material seen escaping from 
manure piles. It is the most valuable portion of the organic matter. 

Treat a portion of this soluble organic matter with hydrate of 
lime. Note the flocculating effect, which prevents the leaching of 
organic matter from the soil. 

Exercise V. — Influence of organic matter on rate of percola- 
tion of water through soils. 




Fig. 12. — Apparatus for studying the influence of the addition of organic 
matter to a soil on the rate of percolation and percentage of water holding 
capacity. 

Materials. — Clay or clay loam soil finely pulverized, moist 
muck, lamp chimneys, torsion balance" and weights, cheesecloth. 

Procedure. — Divide the soil in two portions. To one add 10 per- 
cent of the moist muck. Mix thoroughly. Place equal and definite 



60 SOILS AND FERTILIZERS 

its of the two portions of soil in i. Lamp ohimne; 

having previously tied cheesecloth neatly over the bottoms to ke 
the Boil in place and yet to allow drainage. Compael the soils 
uniform height. Weigh each chimney plus its portion of eh 
Set the chimneys in such a position as to allow free drainage. Po 
equal amounts of water on eaeh and observe the rate ofpercolati 
of the water through the two soils. Explain results and show t 
practical bearing of the experiment. 

Exercise VI. —Influence of organic matter on percentage 
moisture held in -oil. 

Materials. — Same as Exercise V. 

Procedure. — After observing the rate of percolation in t 
above exercise, saturate the soil--, and allow them to drain fret 

until all gravity water has disappeared. Now Weigh each chimn 
plus its soil. The increased weight over that of the original sam] 
is water retained. Calculate the percentage of water thus i 
tained, based on the weight of the original dry sample. Expla 
the practical importance of the results. 



CHAPTER VI 
• SOIL WAT El? 

Of the great number of factors that influence the growth 
of crops none is of more importance., or possibly of as much 
importance, u r on the yield of crops as water. A soil 

may contain too much water for the best growth of crops, or 
y have too little. On the one hand, we approach swamp 
conditions, and on the other the < : bate. Even in the 

same locality and with equal rainfall one field may have 
too much moisture and another too little. While the volume 
of water contained in a «>il depends more or less on the rain- 
fall, it is not controlled entirely by it ; for within a wide 
range of atmospheric precipitation soils of the same type 
may not vary greatly in their moisture content. This is 
"here are other factors beside rainfall that serve 
to regulate the supply of soil water. 

62. Forms of water in soils. — It has already been pointed 
out that in every soil there are spaces between the parti 

or aii. of particles and that the size and total volume 

of these spaces vary with different soils. The 
may be completely filled with water or they may be nearly 
empty. When the pore spaces are entirely filled with water, 
three forms of water are found to be present: (1) hygro- 
scopic, (2) capillary and (3) free or gravitational. These 
forms differ in their relation to the soil particli 

63. How the three forms of water differ. — Xo soil in a 
natural state, that is as it exists in the fields or woo< 

perfectly dry. Xo matter how small the rainfall or how 
61 



62 SOILS AND FERTILIZERS 

parched the crops, there is always a thin film of moisture 
surrounding each particle or aggregation of particles, al- 
though plants may not be able to obtain it. The thin film 
that is absorbed from the air and condensed on the surfaces 
of the particles, when no other source of supply is at hand, 
is termed hygroscopic water. If the film becomes somewhat 
thicker by reason of another supply like rainfall or under- 
ground water, the additional supply is termed capillary 
water. These two forms are much alike, both being held 
as a film around the particles, partly by the attraction of the 
soil for the water and partly by the attraction of the particles 
of the water for each other, which prevents the film from 
breaking and running away. One other difference between 
hygroscopic water and capillary water is that the former is 
always stationary, while the latter may move. 

A further increase in the quantity of water in a soil gives 
rise to the third form — gravitational or free water. With 
the advent of more water, the films become so thick that 
the attraction by which they adhered to the particles is 
overcome by gravity and there is a downward movement 
through the pore spaces, or else the pore spaces are com- 
pletely filled and the soil becomes saturated by reason of 
the inability of the water to escape from the soil. 

64. Hygroscopic water. — From a practical viewpoint, 
hygroscopic water is not of much importance because 
plants cannot use it. A plant may die for want of water 
when the soil in which it grows contains its maximum of 
hygroscopic moisture. The forces that hold the water in 
the soil are greater than those that tend to draw it into 
the plant. 

The quantity of hygroscopic moisture that a soil will 
hold depends largely on its texture and on the quantity of 
partially decomposed organic matter that it contains. Fine 
particles have a greater absorptive power for water than do 




SOIL WATER ' 63 

coarse ones. Clay has a large absorptive capacity and 
the presence of certain compounds increases immensely the 
content of hygroscopic moisture. 

65. Capillary water. — The essential difference between 
capillary water and hygroscopic water is that the former is 
capable of motion and most of it may be used by plants. 
The fact that the capillary film is 

thicker causes it to be less firmly held 
by the soil particles, in consequence of 
which the water near the outer surface 
of the film can move in response to 
certain forces, and the absorptive ac- 
tion of roots is sufficient to withdraw -. ,«, -r>- 

Fig. 13. — Diagram- 
it, Until the film becomes SO thin that matic drawing of soil par- 

very little except hygroscopic water SC™*5 
remains. The difference between hy- lary water, (s) soil parti- 
groscopic water and capillary water is %J$£$S!!?*' **"' 
illustrated in Fig. 13. 

66. Capillary water capacity. — Comparatively large 
quantities of water may be held in soils by capillarity. In 
fact by far the major portion cf water used by crops is ob- 
tained from the capillary form. The quantity present 
varies with different soils and at different times in the same 
soil. The conditions that tend to increase the capillary 
moisture content of soil are the following : 

1. A fine-grained texture, or in other words a large pro- 
portion of small particles. Thus in a test of a fine sand, 
a sandy loam and a clay soil they were found to contain 
respectively 10, 15 and 20 percent of capillary water in 
addition to the hygroscopic water. 

2. A soil structure that gives a maximum effective sur- 
face exposure within the soil. For this reason the granula- 
tion of a clay soil, or the compacting of a coarse sand will 
cause a rise in its capillary capacity. 



64 ' SOILS AND FERTILIZERS 

3. A large amount of partially decomposed organic matter. 
Thus a muck soil may contain a greater weight of capillary 
water than the weight of the dry soil itself. Farm manure 
or green-manures are valuable for this purpose. 

4. A low soil temperature, if it is above the freezing point. 

5. A strong soil solution, such as is produced by proper 
manuring and good tillage. 

6. The absence of oily material produced by decay of 
organic matter. 

The conditions that are favorable to a large crop pro- 
duction are, in general, helpful in increasing the capillary 
water capacity of a soil. The effect of temperature, and of 
oily material formed by decay of organic matter, are excep- 
tions to this. Much may be done by tillage, drainage and 
manuring to increase capillary water capacity. 

67. Movement of capillary water. — The movement of 
capillary water is from particle to particle within the water 
film, the film being continuous from one particle to the other. 
The movement is always from the thicker part of the film 
to the thinner part, because there is a tendency for the film 
to assume the same thickness throughout. Capillary move- 
ment may, therefore, be upward or downward or lateral. 
Following a shower of rain the movement is downward, as 
there is more moisture at the surface than below. Generally 
the movement during the growing season is from the lower 
soil towards the surface, because the roots and surface evapo- 
ration continually remove water from the upper part of the 
soil and this is replenished from the wetter soil below. The 
lateral movement is usually slight. The factors that deter- 
mine the rate of movement of capillary water are much the 
sanie as those that influence its quantity. They are 
(1) texture, (2) structure, (3) height of water column, and 
to a less extent the other factors that influence the quantity 
of capillary water. 



SOIL WATER 



65 



68. Effect of texture on capillary movement. — The finer 
the texture of a soil, other things being equal, the slower 
is the movement of capillary water, but the water will 
eventually rise higher in the soil of fine texture. This is 
illustrated by the experimental data contained in the fol- 
lowing table : 

Table 12. — Effect of Texture on Rate and Height of 
Capillary Rise from a Water Table through Dry Soil 



Soil 


1 Hour 


1 Day 


2 Days 


3 Days 


4 Days 


5 Days 




inches 


inches 


inches 


inches 


inches 


inches 


Sand 


3.5 


5.0 


5.9 


6.8 


6.8 


6.9 


Clay 


.5 


5.7 


8.9 


10.9 


12.2 


13.3 


Silt 


2.5 


14.5 


20.6 


24.2 


26.2 


27.4 



One can see from the above data that although water rises 
most rapidly in the sand, it does not rise as high as in the 
other soils. This experiment was not continued long enough 
to obtain the maximum rise in clay. Some experimenters 
have been able to obtain a rise of water to a height of twenty- 
six feet in a clay soil. 

69. Effect of structure on capillary movement. — Soil 
structure by affecting the size of the pore spaces also affects 
the rate of capillary movement. In general the condition 
most favorable for plant growth is also best adapted to 
capillary movement. Good tillage, tile drainage, farm 
manure and lime all help to hasten the movement of water 
in a soil. A very loose soil does not admit of capillary move- 
ment and consequently cultivation of the surface prevents 
water from coming to the surface of the ground from whence 
it escapes into the air. Rolling, or otherwise compacting 
the soil aids capillary movement and thus causes loss of 
moisture from the surface soil. 



66 SOILS AND FERTILIZERS 

70. Height of water column and capillary movement. — 
Gravity opposes the upward movement of water and conse- 
quently the higher water rises the more slowly it moves. 
This has been demonstrated by measuring the quantity of 
water that evaporated from the surface of columns of sand 
of different heights, the rate of loss by evaporation indicat- 
ing the degree of rapidity of movement. 

Table 13. — Evaporation from the Surface of Sand Columns 

of Different Heights, their Bases being in Contact with 

Free Water 



Height of Column 
in Inches 


Daily Evaporation at Surface in 
Pounds per Acre 


6 


25,872 

25,191 

18,155 

7,716 

4,312 


12 


18 


24 


30 





This has a practical significance in dry weather when the 
moisture supply for plants is drawn largely from the water 
stored in the lower soil. The lower the water level becomes, 
the more slowly does the moisture rise to the surface soil where 
are to be found the larger part of the roots of many plants. 
Fortunately, however, as the soil dries out, the roots go some- 
what deeper, so that they in part overcome this difficulty. 

71. Gravitational water. — It has already been said that 
gravitational, or free water, is the water in excess of the cap- 
illary water and is constantly moving downward, thus pre- 
venting the soil from becoming saturated owing to the 
inability of the water to escape. It is very desirable that 
the gravitational water shall not remain in that part of 
the soil in which plants have their roots. A saturated 
condition of the surface soil is very injurious to most agri- 
cultural plants. In this respect there is a great difference 



SOIL WATER 67 

between gravitational water and capillary water, and while 
it is desirable to have as much capillary water as possible 
in the soil at all times, it is equally important that the gravi- 
tational water shall be removed. 

The factors that determine the rate of flow of gravitational 
water in soil are texture, structure, and cracks and openings 
produced by freezing, by drying, by roots and by the bur- 
rowing of sundry forms of animal life, like worms and 
insects. Another, and very important factor, is the means 
for the escape of water from the subsoil, since without that a 
soil will become saturated no matter how favorable the 
conditions may be for escape of water from the surface 
soil. For this purpose tile drainage must often be used. 

A sandy soil allows the escape of gravitational water more 
rapidly than does a loam or clay soil. Soil in good tilth is 
better in this respect than is compact soil. It is better 
that water should run through a soil than that it should run 
off the surface. The latter generally causes erosion with the 
loss of much good soil, and may leave the subsoil too dry. 
For this reason a loam or clay soil should always have a 
loose surface when no crop is on the ground. 

72. The water table. — The gravitational water that 
passes through the ground accumulates, in humid regions, 
in the lower depths of soil, or possibly in underlying sand 
or gravel, which it saturates. The surface of this mass of 
water is called the water table, the depth of which below 
the surface of the ground varies from a few inches to a great 
many feet, depending on the opportunity it has to escape. 
This is the water that furnishes the supply for shallow wells 
and for springs. In some places the water table is sufficiently 
near the surface to be of use to plants owing to its capillary 
rise during dry periods. 

73. Relations of soil water to plants. — The quantities 
and movements of the several forms of water in soils are of 



68 SOILS AND FERTILIZERS 

the greatest importance in the growth of plants. There are 
certain more or less definite relations that obtain, so that 
for any given condition of the water supply certain results 
in crop growth may be expected. As we shall see later, 
these conditions of water supply are, within certain limits, 
subject to the control of man and consequently the growth 
of crops may be regulated to some extent by these means. 

74. Ways in which water is useful to plants. — In many 
indirect ways water contributes to plant growth, as for 
instance in aiding in the disintegration of rocks, in the pro- 
motion of decay of organic matter and in numerous other 
ways, but it is with the use of water as it occurs in soils and 
as taken up by plants that we are now concerned. The 
functions that water thus serves may be listed as follows : 

1. Water is a direct source of food material, for it either 
becomes a part of the plant substances without change (about 
90 percent of most plants is water), or it is decomposed and 
its elements are used in building plant tissue. 

2. Water acts as a solvent and carrier of plant-food ma- 
terials, taking up these substances in the soil and transferring 
them to the plant, where they are utilized in the formation 
of plant tissue. 

3. Water in the plant serves to keep the cells expanded, 
to regulate the temperature and to carry in solution sub- 
stances from those portions of the plant in which they are 
formed, to the places where they are needed, as for instance, 
to transport soluble matter from the leaves of the potato, 
where the starch is formed, to the tuber, where it is stored. 

75. Water requirements of plants. — Most of the water 
that enters the roots passes on through the plant and evapo- 
rates from openings in the leaves. A large crop will, other 
things being equal, require more water for its production 
than a small crop. The ratio of the quantity of water used, 
to the quantity of dry matter that the plants contain, is 



SOIL WATER 69 

called the transpiration ratio, because the water given off 
by the leaves of the plants is said to be transpired. The 
quantity of water required to produce a pound of dry matter 
varies from 200 to 500 pounds in humid regions to almost 
twice that amount in arid regions. There are a number of 
factors that influence the transpiration ratio. Among these 
are the following : 

1. The kind of plant. 

2. The quantity of water in the soil. 

3. The humidity, wind and temperature of the air. 

4. The natural fertility and manurial treatment of the soil. 

76. Transpiration by different crops. — Some kinds of 
plants require much more water to produce a pound of dry 
matter than do others. Oats, rye, peas and potatoes are 
crops that have a high transpiration ratio. Wheat and 
barley have medium ratios and corn and millet low ratios. 
This, in a way, is a guide to the adaptability of these crops 
to growth on dry soils. 

77. Effect of soil moisture on transpiration. — An increase 
in the water content of any soil usually results in an increased 
transpiration ratio for any crop grown on it. This is well 
brought out by an experiment in which corn was grown in soil 
contained in pots to which different quantities of water were 
added and so maintained during the entire period of growth of 
the plants. The results are expressed in the following table : 

Table 14. — Effect of Soil Moisture on Transpiration 



Soil Moisture 


Transpiration 


Percentage of Total Capacity 


Ratio 


100 


290 


80 


262 


60 


239 


45 


229 


35 


252 



70 SOILS AND FERTILIZERS 

The most economical utilization of water was secured by 
a medium water supply. 

78. Effect of humidity, wind and temperature of the air. 
— A dry atmosphere and a high temperature increase the 
transpiration ratio. For this reason crops require a large 
amount of water in arid regions and in regions of high summer 
temperatures. A high and constant wind movement 
also tends to raise the transpiration ratio. In parts of the 
country requiring irrigation the economical use of water must 
be considered. Such a region is likely to have much sun- 
shine associated with high temperatures and dry atmosphere. 

79. Effect of soil fertility on transpiration. — A soil high 
in available plant-food material has, in general, the property 
of producing crops with a small unit expenditure of water. 
Experiments in Nebraska gave the following results : 

Table 15. — Relative Water Requirements of Corn on 
Different Types of Nebraska Soils 



Soil 


Dry Weight of 

Plants in Grams 

per Pot 


Transpiration Ratio 


Poor ....... 


113 
184 
270 


549 


Medium 

Fertile 


479 
392 







80. Quantity of water required to mature a crop. — A 
rough estimate of the quantity of water required to bring 
to maturity a crop of wheat may be calculated as follows : 
Assuming the yield to be forty bushels or about two tons of 
dry matter in straw and grain and the transpiration ratio 
to be 400, the quantity of water actually used by the plants 
would be 800 tons to the acre, or equivalent to about 7 
inches rainfall. In addition to this there would be an equal 
or larger quantity of water evaporated directly from the 



SOIL WATER 71 

soil. The annual amount of rainfall required for crop- 
production is brought to a much higher figure by the loss 
due to run-off and percolation. 

81. Capillary movement and plant requirement. — We 
have seen that there is a capillary movement of water from 
the more moist to the less moist soil. As water is absorbed 
by plants, the moisture content is reduced in the soil sur- 
rounding the root-hairs by which the moisture is taken up. 
Immediately a movement begins to establish equilibrium 
in the water films and during the time the roots continue to 
absorb moisture, the movement of capillary water goes 
on. During the blooming period, plants must have very 
large quantities of water if they are to develop fully and 
produce large yields of grain. Capillary movement is 
necessarily slow, especially in heavy loam and clay soils. 
It is often impossible for the capillary movement to carry 
moisture fast enough, except for short distances, to supply 
plants adequately and the crop suffers for want of moisture. 
In a dry season the capillary capacity of a soil is likely to 
be of more importance than the rate of capillary movement, 
as the supply is more easily available. Hence, in time of 
drought a loam soil in good tilth is better than a sandy 
soil. 

82. Optimum moisture for plant growth. — Plants wilt 
for want of water at a moisture content somewhat higher 
than that represented by hygroscopic moisture. They 
show the pale color characteristic of too much moisture 
when a soil is saturated. Before either of these well-known 
signs of distress is shown, the plant may have too much or 
too little water to allow of its maximum growth. The 
optimum moisture content lies somewhere within the range 
of capillary moisture. It is variously stated by different 
experimenters to lie between 60 and 90 percent of the water 
capacity of soils. Probably it varies with different soils. 



72 SOILS AND FERTILIZERS 

The range is doubtless greater for a soil in good tilth than 
for one in poor condition, and the wider the range of 
optimum moisture content the less likely is a crop to suffer 
from either extreme. 

83. The control of soil moisture. — Since there may be 
too much or too little water in a soil for its most effective 
crop production, the problem of moisture control is to remove 
the excess and to conserve the remainder, attempting- to 
maintain the supply within the range of the optimum mois- 
ture content. In heavy soils there is likely to be a surplus 
of water in the spring and in sandy soils a deficit in midsum- 
mer. The excessive water content in the spring is also 
objectionable because it delays plowing, planting, and germi- 
nation of seed as well as the early growth of crops. The 
ways in which water leaves soil are by (1) run-off over the 
surface ; (2) percolation ; (3) evaporation ; (4) absorption by 
plants. The last of these is to be encouraged, at least when 
it is economically accomplished. Run-off should generally 
be prevented. Percolation and evaporation should be con- 
trolled within certain limits. 

84. Run-off. — Removal of water in this way is objection- 
able because the rivulets carry with them the fine particles, 
which are frequently the most valuable part of a soil, and 
gullies are formed that ma} r interfere with the working of 
the land. In regions in which the rainfall is large, and 
particularly where it falls in torrential showers, more than 
half of the precipitation may escape in this way. The 
water so removed is, of course, entirely lost so far as its 
utilization by plants is concerned. The proportion lost by 
run-off is greater on slopes than on level land, and on com- 
pact soil than on sandy soil or on soil in good tilth. 

The removal of excess water by means of open ditches is, 
to some extent, a utilization of run-off to drain land, but 
it is not so desirable a method as tile drainage. It is better 




Plate VIII. 



Forms of Erosion. — Erosion of soil by water in upper 
figure. Erosion by wind in lower. 



SOIL WATER 73 

to have the moisture pass into the soil and this is encouraged 
by any of the operations and conditions that favor the main- 
tenance of good tilth. Fall plowing and early spring plow- 
ing also serve this end. In arid and semi-arid regions run- 
off is usually not of any moment. Terracing a hillside is 
often resorted to as a preventive of run-off, especially in 
the south Atlantic states where the rainfall is often tor- 
rential. 

85. Percolation. — Water that enters a soil is either 
retained by the capillary spaces or eventually percolates 
into the subsoil. The percolate is lost to crops, except that 
part which remains in the subsoil and is later raised by 
capillarity to within reach of roots. The chief consideration 
is to maintain the soil in good tilth, which gives a large 
capillary capacity, thus storing within easy reach of the 
roots a maximum quantity of the descending water. The 
more rapidly the gravitational water is disposed of the better, 
because its presence prevents aeration of the soil together 
with those beneficial processes that good ventilation encour- 
ages. One of the most frequent causes of saturation of soil 
is lack of facility for the water to escape from the lower 
depths. This difficulty is best relieved by tile drainage. 

86. Evaporation. ■ — It has been concluded from experi- 
ments conducted at Rothamsted, England, that with an 
annual rainfall of twenty-eight inches, one-half is lost by 
percolation. The quantity of water required to produce an 
average crop in a humid region is about seven inches, which 
is one-balf of the water retained by the soil. The other half 
is presumably lost by evaporation. A rough estimate of 
the disposition of rain water in a humid region would there- 
fore be one-half lost by percolation, one-fourth by evapora- 
tion and one-fourth used by the growing crop. The ratio 
of quantity lost by evaporation to quantity used by crop 
may vary by reason of a number of factors, among which is 



74 SOILS AND FERTILIZERS 

the ease with which evaporation may take place. Moisture 
saved from evaporation is at the immediate disposal of the 
crop. 

87. Mulches for moisture control. — Any material ap- 
plied to the surface of a soil primarily to prevent loss by 
evaporation may be designated as a mulch. It may at the 
same time fulfill other useful functions, like keeping down 
weeds and maintaining a uniform soil temperature. The 
mulch ordinarily used for fallow land is produced by stirring 
the surface soil. Mulches may be formed of straw, leaves, 
flat stones, cloth, sawdust and various other materials, but 
the most practical material is soil. 

88. The soil mulch. — The soil mulch is made by stirring 
the surface of the soil with some one of the ordinary tillage 
implements. For fallow land a disk harrow, straight, or 
spring tooth harrow may be used. For intertilled crops 
numerous forms of cultivators are made for the special pur- 
pose of going between the rows of plants. For small grain 
a weeder or spike-tooth harrow, with the teeth slanted back- 
ward, is frequently used while the grain is young. This 
practice has much to recommend it in an arid or semi-arid 
region. 

In making a soil mulch the object is to destroy the capil- 
larity near the surface soil and thus to prevent the move- 
ment to the surface of water from the portion of the soil 
below the mulch. Stirring may accomplish this by breaking 
up the cohesion of particles to such an extent that moisture 
cannot pass from one to the other. 

89. Frequency of stirring. — Some kinds of soil re- 
quire more frequent stirring than others. For instance, 
a sand will maintain a mulch longer than a loam or clay. 
The latter becomes moist from below and will gradually 
allow moisture to reach the surface. Rain will also compact 
a mulch and unless it is soon restored there may be more 



SOIL WATER 75 

moisture lost than was received as rain. While it is not 
possible to make a definite rule for frequency of stirring a 
mulch, it may be said that a mulch should never be allowed 
to remain in a compact condition. However, in arid regions 
the surface of the soil sometimes becomes completely dry 
so quickly, even when compact, that capillary connection 
is destroyed and loss of moisture is prevented. 

90. Depth of mulch. — In considering the depth that a 
mulch should have, several facts should be kept in mind. 
The deeper the mulch the more effective it will be, but as 
it must be perfectly dry, roots cannot obtain nourishment in 
the zone occupied by the mulch. The surface soil, from 
which plants derive a large part of their material, is frequently 
only eight to ten inches deep in humid regions and the deeper 
the mulch the less top soil remains for roots. In arid regions 
plants obtain food materials from greater depths and mulches 
may be made deeper, which is fortunate since they need to 
be deeper in regions where evaporation is greater. Another 
consideration is the disturbance of roots in the process of 
cultivation. Here, again, there is less occasion to cultivate 
shallow in an arid region, as roots are generally found at 
greater depths in such soils. 

A good depth for a mulch in humid regions is about three 
inches, becoming somewhat less during the last cultivations 
of corn. In irrigated regions a mulch of ten to twelve inches 
is frequently used, especially in orchards, in which it is often 
not necessary to renew the mulch, as the rainfall is usually 
light. 

91. Effectiveness of mulches. — That mulches are effec- 
tive in conserving moisture and increasing crop yield has 
lately been called in question by certain writers who claim 
that corn is not more benefited by tillage than by the 
removal of weeds without tillage, and by some experi- 
menters who find that fallow land contains as much moisture 



76 



SOILS AND FERTILIZERS 



when weeds are removed by scraping the surface of the 
ground as when the soil mulch is maintained. It seems 
possible that the latter result may occur only in those 
regions in which conditions are such that a natural mulch is 
formed by the rapid drying of the surface soil, in which 
process moisture is removed so quickly that the capillary 
column is broken and further loss of moisture is stopped. 
This would confine it to semi-arid and arid regions of high 
summer temperatures. 

The failure of the soil mulch to conserve moisture in corn 
land has been explained on the supposition that the corn 
roots ramifying through the upper soil absorb so much 
water that they cut off the upward movement as effectually 
as does a mulch. The results of some experiments in 
semi-aricl Montana indicate a high degree of usefulness for 
the mulch. 

Table 16. — Moisture Content of Mulched and Unmulched 
Eastern Montana Soils. Average of Three Years 



Depth of Sample 


Percent Moisture in Soil on Oct 6. 




Mulched 


Unmulched 


First foot 


16.8 


10.8 


Second foot 


16.4 


9.4 


Third foot 


13.2 


9.5 


Fourth foot 


10.1 


8.9 


Fifth foot 


9.6 


8.5 


Average 


13.2 


9.4 



The investigator comments on these results as follows : 
" If the wilting point of this soil is 6 percent, the mulched 
area contains more than twice as much available moisture. 
This 3.8 percent of available moisture by which the mulched 
soil excels the unmulched is equivalent in a five-foot depth 
to about 250 tons of water, enough to increase the crop by 
a ton of dry matter." 



SOIL WATER 



77 



92. Other devices to prevent evaporation. — Plowing in the 
early spring or immediately after taking off a crop of 
small grain is a means of preventing evaporation. In regions 



E.£?OAPirs<b M( 




Fig. 14. — The effect of a soil mulch is to break up the capillary spaces 
within the mulch itself and thus to prevent the upward movement of water 
through it. Water, therefore, remains in the lower soil instead of evaporat- 
ing from the surface. This condition is shown in the right-hand column. 
When no mulch is maintained the soil dries at the surface and then cracks, 
which allows it to dry more rapidly below. 



in which grain crops suffer for moisture in the early spring, 
it is not uncommon for farmers to harrow the small grain, 
following the drill rows with a spike-tooth harrow with its 
teeth turned backwards. This practice is likely to be very 
beneficial. 



78 SOILS AND FERTILIZERS 

Windbreaks are effective in decreasing evaporation by 
lessening the velocity of the wind. King found that evapora- 
tion from a moist soil was twenty-four percent less at a dis- 
tance of twenty to sixty feet from a black oak grove than it 
was about three hundred feet distant. 

93. Rolling and subsurface packing. — These operations 
are resorted to in order to bring moisture to the surface or 
upper layer of soil. Rolling compacts the superficial layer 
of soil and thus establishes capillary connection with the 
moist soil below. This may be desirable in order to bring 
moisture in contact with seeds, but although germination 
is hastened loss of moisture results. 

Subsurface packing is designed to make more compact a 
naturally loose soil by running wedge-rimmed wheels through 
it. If the soil is too loose for capillary movement of water 
to proceed effectively, this operation promotes it. Its use 
is confined to arid or semi-arid regions. 

94. Removal of water by drainage. — Land drainage is 
any condition, natural or artificial, that enables the surplus 
water to escape from soils. A soil may be highly productive 
when drained, but worthless before draining. This is but 
another illustration of the many factors affecting soil pro- 
ductiveness. Where natural drainage is poor, artificial 
drainage is generally a profitable investment. It may be 
accomplished either by surface ditches or by underground 
drains. 

95. Benefits of drainage. — There are many ways in 
which good drainage benefits soils and crops. The need of 
drainage may be very evident in the yellow color and poor 
growth of young plants, or it may be less readily detected, and 
yet may be sufficiently needed to make it a profitable invest- 
ment. Good drainage is the first requisite in enabling a soil 
to reach its maximum productiveness. The principal ways 
in which drainage benefits the soil and crop are as follows : 



SOIL WATER 79 

1. Enlargement in the supply and movement of soil air. 

2. Improvement in tilth. 

3. More available water throughout the growing season. 

4. Longer growing season. 

96. Soil air. — Drainage increases the supply and move- 
ment of soil air by allowing the gravitational water to run 
off and thus to be replaced by air. With each fall of rain 
there is a movement of air through the soil. The increased 
air supply is of benefit in the following ways : 

1. It furnishes air to roots which require it for the proper 
performance of their functions. 

2. It facilitates the decomposition of organic matter of 
all kinds, thus disposing of the vegetable matter incorporated 
with the soil, and permitting the most beneficial kind of de- 
composition (see §§ 59, 60). 

3. It furnishes the conditions necessary for the trans- 
formations of nitrogen in the soil which prepare that sub- 
stance to be used by plants (see §§ 116-168). 

97. Soil tilth. — Alternate drying and wetting of soil is 
one of the processes that causes the formation of granular 
structure and consequent improvement of tilth. A soil 
that is constantly saturated or very wet when worked in 
the spring assumes a compact condition. The larger air 
space reduces heaving by allowing expansion of freezing 
water within the soil, and diminishes the tendency to erosion, 
by allowing water to sink quickly into the soil, instead of 
running over the surface. 

98. Available water during the growing season. — A soil 
in need of drainage is often in need of moisture in midsummer, 
because when it does dry out its water-holding capacity 
is low, on account of its compact condition. Furthermore, 
plants form shallow roots in a saturated soil, and if the 
weather becomes dry later in the season, the roots do not 
then go to the depth necessary to reach the water supply. 



80 SOILS AND FERTILIZERS 

It frequently happens, therefore, that plants suffer much 
from lack of moisture on a soil that has been saturated with 
water during the early part of the growing season. 

99. Length of growing season. — Drainage increases 
the length of the growing season in two ways : (1) The soil 
can be worked much earlier than on poorly drained land. 
(2) The soil becomes warm earlier, because it is easier to heat 
soil particles than it is to heat water. Then too the evaporat- 
ing moisture causes a lowering of the soil temperature. 
Seeds germinate more quickly and uniformly and plants 
make a more rapid growth on account of the warmer soil. 

100. Other results of drainage. — All of these improved 
conditions unite to produce larger yields of crops and more 
uniform growth. Drainage eliminates the continually 
wet or swampy portions of fields that interfere with tillage 
operations and necessitate working the field in sections. 
There is, accordingly, an economy in operation. In meadows 
and pastures the kinds of forage plants that grow on a well- 
drained soil make better feed than those kinds that grow 
on wet land. 

101. Open ditches. — Excess water is sometimes removed 
by means of open ditches of size and depth necessary to 
drain water from the land and carry it to some waterway. 
Such ditches sometimes merely follow a depression or swale 
in the land and thus carry off the worst of the excess water, 
especially that which comes from higher land, or they are 
sometimes laid out in a more systematic way. 

Level fields may be plowed in lands with dead furrows 
every twelve to twenty feet apart, and with a larger ditch 
run through lower ground for the dead furrows to empty 
into. This affords only surface drainage, but is better 
than nothing. Larger ditches should have grass planted 
along the sides for several feet from the ditch. Weeds must 
be mowed and trash, dirt and stones removed at intervals. 



SOIL WATER 81 

Open ditches require much labor to keep them in order, 
they do not remove the water so thoroughly as do tile drains, 
and they not only occupy a considerable area but they inter- 
fere with the cultivation of much land on account of the 
space along the ditches required for turning the teams in 
cultural operations. Only under exceptional conditions may 
open ditches be profitably used instead of tile drains. 

102. Tile drains. — These drains are composed of baked 
clay or hardened concrete cylinders with open ends, their 
length being about one foot and their diameter varying 
from three inches to eight or more. These tiles are laid 
end to end on the bottom of ditches two to four feet in depth, 
having a fall sufficient to carry off the water and prevent 
the tiles from becoming clogged with soil particles. Tile 
should not be made of clay that contains particles of lime, as 
the lime when baked is converted into quicklime, which 
causes the tile to crumble when buried in the soil. 

It is not necessary that tile shall be permeable to water, 
as it is through the openings between the ends of the tile 
that water enters, and not through the pores. Vitrified 
tile may well be used, as they are less likely to be injured 
by freezing than are porous tile, because expansion of ab- 
sorbed water on freezing causes the latter to disintegrate. 

Concrete tile are often used and these may be made on 
the farm, with forms constructed for the purpose. 

Silt and fine sand may enter the tiles through the open- 
ings between them, and to guard against this collars are 
sometimes placed over the joints, but with proper grades 
this is not necessary. Sometimes tile are hexagonal on the 
outside, for the purpose of preventing settling of the tile 
in places, with a consequent stoppage with silt. However, 
if the bottom of the ditch is carefully made, round tile are 
not likely to deviate from alignment and they are more easily 
laid. 



82 



SOILS AND FERTILIZERS 




103. Arrangement of drains. — In laying out a system 
of drains certain rules must be regarded. A main drain 
usually follows a depression in the land, rising with the 

natural grade, or 
if that does not 
give a sufficient 
rise, becoming 
shallower as it 
ascends. Some- 
times this will be 
sufficient to re- 
move the surplus 
water, but more 
often lateral 
drains will be nec- 
essary. These are 
of smaller tile and 
are usually paral- 
lel to each other 
and from twenty 
to a hundred feet 
apart. This ar- 
rangement is 
called the herring 
bone system. 
(See Fig. 15.) 
There may also be 

Fig. 15. — The upper drawing illustrates the her- SUbmains branch- 
ring bone system of laying tile drains. The lower ing off of the main 
represents the gridiron system. ^.^ ^ ^^ 

running into the submains. This is known as the gridiron 

system. (See Fig. 15.) Sometimes the laterals are run 

across the slope, but usually it is better to run them down. 

A lateral should not enter a main drain at a right angle, 






Plate IX. Drainage. — The drain outlet is often poorly constructed 
and easily clogged, as shown in the upper figure. The lower one is well 
protected. 



SOIL WATER 83 

but an acute angle should be formed between the two streams 
above the point of contact ; ' otherwise the flow of water 
will be impeded. For the same reason two laterals should 
not enter a main drain opposite to each other. 

It is desirable to have as few main drain outlets as possible, 
for the outlet is likely to be the weakest point in a drainage 
system. If it becomes clogged, the entire system is put 
out of action. It is more likely to be injured by freezing 
than is the underground tile, and unless well protected it 
affords an opening into which small animals may crawl and 
clog the system. 

The quantity of water removed by tiles of various sizes, 
and laid at certain distances and grades as well as other 
operations that cannot be treated here, may be ascertained 
from the books that deal exclusively with the subject of land 
drainage. 

104. Digging ditches and laying tile. — The depth of 
ditches for tile drainage varies from two to four feet. Three 
feet is the usual depth. The closer together the laterals, 
the shallower the drains may be laid. A compact soil, 
through which water moves very slowly, will require the 
use of shallow drains. A lighter soil underlaid by hardpan 
will also require shallow drains. The shallower the drains 
in any soil, the closer together they must be laid, the cus- 
tomary range being from twenty to a hundred or more feet. 
Surplus water enters the drains from the soil immediately 
surrounding them. As the larger pore spaces become 
partly empty, water enters them from surrounding soil, 
and in this way drainage gradually extends. The soil mid- 
way between the drains is the last to lose its surplus water, 
and the water table is always higher between drains than 
over them. 

The distance between drains must be small enough to 
allow the water table to descend promptly to a point where 



84 



SOILS AND FERTILIZERS 



it will not interfere with root growth. The more permeable 
the soil and the deeper the drains, the further apart they may 



•SC/azf/zce: 



^|r 





Fig. 16. — Cross sections of two soils, a sandy loam and a clay, both of 
which have drain tiles laid at right angles to the sections. Owing to the 
more rapid movement of water through the sandy loam, the tiles are laid 
twice as far apart as they are in the clay. They are also deeper in the former 
soil. The water gradient is steeper in the clay. The tiles should be suf- 
ficiently close together to keep the water table below the plowing line. 

be placed. The position of the water level between drains 
is shown in Fig. 16. 

Ditches may be dug or partly dug by means of spades, 
ditching plows or traction ditchers. The last named, while 

Trie Elements or Soil Water Control 



WATER CONTROL 



MOISTURE CONSERVATION 



DRAINAGE 



WILTING POINT 

: r~ 



\ OPTIMUM 501L MOISTURE \ 

UNAVAILABLE t AVAILABLE 

WATER WATER 



MAXIMUM CAPILLARY 
CAPACITY 



5URPLUS 
WATER 



Fig. 17. — Diagrammatic explanation of water control in a humid region. 
On the one hand we have drainage reducing the surplus water to the maxi- 
mum capillary water capacity or below and thus bringing it within the range 
of available water. On the other we have moisture conservation by means 
of which the moisture is kept above the content of unavailable water or the 
wilting point. Somewhere within the limits of available water lies the 
optimum moisture content for plant growth. 



SOIL WATER 85 

expensive in first cost, is economical in operation in many 
soils. After the ditch has been opened to its full depth, 
it is necessary to go over the entire bottom to remove loose 
dirt and to give it the necessary grade. This must be done 
by hand. Either a ditching spade or a drain scoop is the 
best implement to use. A fall of at least four inches in a 
hundred feet is necessary under most conditions, but in 
clay soils less fall is permissible, as there is less danger of 
silt entering the drains. 

QUESTIONS 

1. Name the three forms in which water is present in soils. 

2. Explain what is meant by hygroscopic water. Capillary 
water. Gravitational water. 

3. On what does the content of hygroscopic water depend ? 

4. Name six conditions that tend to increase the capillary 
water capacity of soil. 

5. Explain the relation of soil texture to the movement of 
capillary water. 

6. How does soil texture affect the rate of movement of 
capillary water ? 

7. What are the conditions that affect the rate of flow of grav- 
itational water ? 

8. Explain what is meant by the water table. 

9. Describe three ways in which water contributes directly to 
plant growth. 

10. What is the transpiration ratio ? 

11. Name three factors that influence it. 

12. Calculate the number of inches of rainfall transpired by a 
three-ton crop having a transpiration ratio of 250. 

13. Name four ways in which water leaves soil. 

14. What is the principle of the soil mulch ? 

15. State four ways in which drainage benefits soils. 

LABORATORY EXERCISES 

Exercise I. — Determination of the percentage of water in a soil. 
Materials. — Samples of moist soil, torsion balance, evaporating 
dishes, air oven and flame, desiccator. See Plate IX. 



86 SOILS AND FERTILIZERS 

Procedure. — Carefully obtain the weight of an evaporating dish 
on the balance. Then weigh into the dish 50 grams of the soil to 
be tested. Air dry sample in laboratory and then place it in air 
oven at 100° C. for two hours. Cool in desiccator and weigh. The 
loss in weight is water. Calculate the percentage of moisture 
based on absolutely dry soil. 

Make this determination in duplicate and on a number of soils. 
Calculate the amount of water in an acre foot of the various soils, 
considering them to weigh 3,500,000 pounds per acre foot. Note 
relation of soil moisture content to bare and cropped soil, kind of 
crop, stage of growth and previous rainfall. 

Exercise II. — Capillary movement in different soils. 

Materials. — Dry samples of pulverized sandy loam, silt and 
clay, three long glass tubes 2 inches in diameter, pans for water and 
cheesecloth. See Plate IX. 

Procedure. — Neatly cover the ends of the three long glass cylin- 
ders by tying over them two thicknesses of cheesecloth. Pill cylin- 
ders with the respective soils to be studied. Be sure that the 
compaction is uniform. Now set the ends of the cylinders in water 
one inch deep and observe the height of capillary movement at the 
following periods after starting : 1 hour, 2 hours, 12 hours, 1 day, 
2 days, 3 days, 4 days, etc. Continue experiment as long as prac- 
ticable. Tabulate data and draw curves. Explain the practical 
importance of the results obtained. 

Exercise III. — Rate of percolation of water through soils. 

Materials. — Dry, well-pulverized sand and clay loam, two lamp 
chimneys, cheesecloth, torsion balance. See Exercise V, Chapter V. 

Procedure. — Prepare two lamp chimneys by neatly tying two 
thicknesses of cheesecloth over their bottoms. Place in one a 
definite and known amount of sand. In the other place the same 
weight of clay loam. Give each a uniform compaction. Now weigh 
each chimney with its content of soil. 

Place the chimneys in such a position as to allow free drainage 
and add the same amount of water to each, keeping the head of water 
constant in each chimney. Observe the rate of the downward 
movement of water through the two soils. When percolation has 
begun, measure percolate for 15 minutes and express rate in cubic 
centimeters per hour. 

Explain the reasons for the results obtained and the practical 
importance thereof. 





1 • 


s 






H 



'C rt 



U +3 

go 



CO CO 

"3) £ 



Ot3 




SOIL WATER 87 

Exercise IV. — Water-holding capacity of soils. 

Materials. — Same as in Exercise III. 

Procedure. — When Exercise III is complete, cover chimneys and 
allow all the free water to drain away. Then weigh the chimneys 
and wet soil. The increased weight is water retained. Calculate 
the percentage of water retained by each soil based on the weight 
of the original sample. 

Write out a full description of the experiment and the points 
of importance that it shows. 

Exercise V. — Moisture conservation by means of a soil mulch. 

Materials. — Three tumblers, one of which should be one inch 
shorter than the other two, moist soil, dry clay loam and dry sand, 
torsion balance. 

Procedure. — Fill the short tumbler level full with a well-mixed 
moist soil. This is to serve as the unmulched treatment. Place 



CLAY LOAM MULCH 5AMDY LOAM MULCH 



MULCH 

I 




MOI5T50IL M0I5T SOIL M0I&T50IL 

Fig. 18. — Tumblers filled with equal quantities of a moist soil and pre- 
pared for a demonstration of the effectiveness of mulches in the conserva- 
tion of moisture. Losses of moisture by evaporation are measured by weigh- 
ing the tumblers. 

exactly the same amount of moist soil in each of the other tumblers 
as is used in the shorter one, compacting to within one inch of the top. 
On the surface of one place one inch of dry clay loam and on the 
other one inch of dry sand. Weigh the tumblers now fully prepared. 

Set tumblers in a place of uniform temperature and weigh daily 
for a week. The loss of weight each day is moisture. Tabulate 
data and draw curves. 

Explain the significance of the results obtained. 



88 



SOILS AND FERTILIZERS 



Exercise VI. — Loss of water by transpiration. 
Materials. — Glazed gallon butter jar, oats seed, paraffined paper, 
thistle tube, coarse sand and heavy balance. 

Procedure. — Fill a glazed jar with rich soil, first adjusting coarse 

sand and thistle tube as shown in 
Fig. 19. Moisten soil with water, 
but not too wet, and plant with oat 
seed. When seedlings are one week 
old, thin to suitable number. Then 
cover surface of soil with paraffined 
paper, allowing plants to protrude 
through small holes cut for that pur- 
pose. Paraffine the paper to side of 
jar so that all losses of moisture by 
evaporation may be prevented. 
Bring soil up to optimum water con- 
tent and weigh. You are now ready 
to record losses by transpiration. 

Weigh jar each week, replacing 
water lost through the thistle tube. 
Record data and draw curves. By 
changing the jar from sunshine to 
shade, warm temperature to cold, 
high humidity to low, etc., the fac- 
tors influencing transpiration may 
be studied. 

Jars with different crops, different soil or the same soil with differ- 
ent fertilizers or different water treatments may be utilized if so 
desired. 

Exercise VII. - — Review problems. Chapters IV and VI. 

1. A soil weighs 100 lbs. per cubic foot when dry. The weight 
of a cubic foot of water is 62.5 lbs. Calculate its apparent specific 
gravity and weight per acre foot. Ans. 1.6 and 4,356,000 lbs. 

2. This soil has an absolute specific gravity of 2.7. Calculate 
its pore space. 

% pore space 




Fig. 19. — Glazed jar equipped 
for observation of transpiration 
of water from plants, (a) thistle 
tube for watering, (b) plants, (c) 
paraffined paper to prevent evap- 
oration from the soil surface, (d) 
soil, (e) gravel. 



100 



T ap, sp. 



Labs. sp. gr 



gr. x 1001 



Ans. 40.7+% 



3. This soil contains 10 pounds of water a cubic foot. Calculate 
percentage of water based on absolutely dry soil. On wet soil. 

Ans. 10 % and 9.09 %. 



SOIL WATER 89 

4. By the following formula, calculate the air space present. 

% air space = % pore space - ( % water X ap. sp. gr.) Ans. 24.7 %. 

5. The wilting point in this soil is 4 percent. What is the per- 
centage of available water ? Weight of available water per cubic 
foot ? Per acre foot ? Ans. 6 %, 6 lbs. and 261,360 lbs. 

Exercise VIII. — Tile drainage. 

If possible, have the class install a short drainage system. They 
should dig at least part of the ditch, grade the bottom, lay the tile 
and build the outlet. The explanation of every point involved as 
the work proceeds will give such an exercise great practical value. 
It will also make the classroom work much more effective. 

If drainage operations are being conducted in the near vicinity, 
the class should by all means be taken to inspect them. The 
general plan of the work, as well as the more detailed phases, should 
be explained by the teacher. Materials and illustrations may also 
be obtained for later discussion and study in the classroom. If 
ditching machinery is being utilized, it also should be given consider- 
able study. 

Early in the spring, while the soil is still wet, a field trip might 
well be taken. The need of drainage, the movement of water 
through soil, the effectiveness of drainage, the entrance of water into 
a drainage system, the movement of water through tile, good and 
poor outlets and the drainage of roads could be studied with profit. 



CHAPTER VII 
PLANT-FOOD MATERIALS IN SOILS 

Plants secure their mineral food materials exclusively 
from the soil. In a state of nature plants at death fall 
on the surface of the ground and as decay proceeds, their 
ash constituents return to the soil. The loss of mineral 
matter, under these conditions, is due almost entirely to 
its solution and removal in drainage water, or to erosion. 
Under ordinary farm practice the procedure is different. 
The aboveground portions of plants are removed wholly, 
or in part, from the land and the loss of easily soluble min- 
eral matter is thus greatly increased. The soil supply of 
those particular elements required for the growth of crops 
is a matter of great importance, for it is upon this that man 
must depend for his sustenance, and although he may 
supplement these elements in the soil by the use of manures, 
the cost of food is thereby materially increased. 

105. Variations in content of plant nutrients in different 
soils. — There are wide differences in the quantities of plant- 
food materials in soils from different localities, although 
the localities may be near together. This is illustrated by 
the following statement of the analyses of soils from different 
parts of the country, the number of pounds of each ingredi- 
ent being based on" the weight of 2,000,000 pounds of soil, 
which is about the weight of the furrow slice of an acre of 
land. 

90 



PLANT-FOOD MATERIALS IN SOILS 



91 



Table 17. — Composition of Some Arable Soils Based on 
Ultimate Analyses 





Pounds in 2,000,000 Lbs. 


of Soil 


Percentage Composition 


Location 


Nitro- 
gen 


Phos- 
phoric 
Acid 


Potash 


Lime 


Nitro- 
gen 


Phos- 
phoric 
Acid 


Potash 


Lime 


New York 


2,520 


1,680 


40,200 


6,600 


0.126 


0.084 


2.010 


0.330 


New York 


2,860 


1,620 


33,400 


4,600 


0.143 


0.081 


1.670 


0.230 


New York 


2,800 


3,280 


17,200 


68,400 


0.140 


0.164 


0.860 


3.420 


New York 


4,000 


3,920 


39,200 


5,400 


0.200 


0.196 


1.960 


0.270 


Ohio l . . 


1,260 


966 


43,975 


11,303 


0.063 


0.043 


2.198 


0.565 


Ohio » . . 


3,844 


14,008 


67.285 


, 78,772 


0.192 


0.700 


3.364 


3.938 


Ohio ! . . 


186 


3,106 


37,214 


15,478 


0.009 


0.155 


1.860 


0.773 


Ohio » . . 


2,974 


1,580 


37,070 


4,480 


0.148 


0.079 


1.853 


0.224 


Illinois 2 . 


6,480 


4,145 


42,493 


28,644 


0.324 


0.207 


2.124 


1.432 


Illinois 3 . 


6,020 


3,710 


39,165 


104,636 


0.301 


0.185 


1.958 


5.232 



The soils whose analyses are stated in the table given above 
are all from arable land and while they represent wide differ- 
ences in some of their constituents none of them is so deficient 
in any plant nutrient as to prevent it from producing crops. 
Comparing the quantities of the constituents of these soils, we 
find that in the Illinois soils the lime varies from 28,644 
pounds to 104,636 pounds in 2,000,000 pounds of soil. In Ohio 
the same constituent ranges from 4480 to 78,772 pounds 
with nearly as low a minimum in New York. The nitrogen 
in Ohio rises from a minimum of 186 pounds to a maximum of 
3844 pounds while the maximum for Illinois is 6480 pounds. 
The greatest range of phosphoric acid is from 966 pounds to 
14,008 pounds, both of which soils occur in the same state. 

Another fact brought out by this table is that a soil may 
be rich in one ingredient and poor in another, also that soils 
lying near together may differ more in composition than do 
soils that are widely separated. 



1 Ohio Experiment Station Bui. 261. 
3 Illinois Soil Report No. 10. 



8 Illinois Soil Report No. 2. 



92 



SOILS AND FERTILIZERS 



106. The total supply of plant-food materials. — The 
statement of analyses in Table 17 shows the quantities of 
plant nutrients in 2,000,000 pounds, which represents the 
weight of an acre of soil to a depth of only six to eight inches. 
There is below this a considerable volume of soil through 
which roots ramify, and from which some nutriment is 
drawn. The roots of ordinary crops extend to a depth of 
three or four feet into the soil, depending on different condi- 
tions of soil and climate. In semi-arid and arid regions 
roots extend deeper than they do in humid regions, and in 
well-drained soils they penetrate deeper than they do in 
poorly drained ones. It is, however, from the furrow slice 
that plants derive most of their nourishment. 

Subsoils sometimes contain more and sometimes less 
plant-food materials than do the surface soils. Nitrogen 
is almost always present in greater quantity in the surface 
soil, because, it is a constituent of material that has been 
plowed into the furrow slice. Table 18 contains a statement 
of the analyses, expressed in percentage composition, of two 
soils to a depth of four feet, each foot of which was analyzed 
separately. 



Table 18. — Ultimate Analyses of Two Soils to a Depth of 
Four Feet, Expressed in Percentage Composition 





Dunkirk Clay Loam 


Volusia Silt Loam 




1st ft. 


2nd ft. 


3rd ft. 


4th ft. 


1st ft. 


2nd ft. 


3rd ft. 


4th ft. 


Nitrogen . . 


.126 


.067 


.064 


.064 


.143 


.052 


.059 


.050 


Phosphoric 


















acid 


.084 


.066 


.103 


.125 


.081 


.039 


.018 


.071 


Lime . . 


.330 


.270 


.520 


1.780 


.230 


.160 


.260 


.360 


Magnesia 


.160 


.150 


.15u 


.320 


.560 


.390 


.290 


.400 


Potash . . 


2.010 


2.480 


2.550 


2.630 


1.670 


1.790 


2.000 


2.140 











Plate XI. Surface Soil and Subsoil. — Note the difference 
between the top soil and the subsoil in the upper figure ; also the abun- 
dant growth of plant roots in the top soil as compared with the subsoil in 
the lower figure. 



PLANT-FOOD MATERIALS IN SOILS 93 

These analyses show in some cases more, and in others 
less, of the various constituents below the surface foot, 
with the exception of nitrogen, which is always less in the 
subsoil. The fact that the greater part of the roots of 
most plants is in the surface soil makes the draft greater 
on that layer, but the total volume to a depth of four feet, 
or even more, may be considered to be the feeding ground 
of crops. 

107. Upward movement of plant-food materials. — There 
is another way in which the soil to a considerable depth 
may contribute to the nourishment of crops. This is by 
furnishing plant-food materials that are carried upward 
by ascending currents of moisture, or that are absorbed by 
roots from the lower depths and deposited near the surface 
when the plants die. To what extent the upward movement 
due to moisture is operative is something of a question ; 
in humid regions probably very slightly, in semi-arid and 
arid regions it is doubtless of considerable moment, as indi- 
cated by the existence of alkali crusts. 

108. Plant nutrients compose a small part of the soil. — 
Another point brought out by Table 17 is the very small 
proportion of the soil that is represented by plant-food ma- 
terials. For instance, the sum of all of the nitrogen, phos- 
phoric acid, lime, magnesia and potash is not much more 
than two percent of the total weight of the soil, and it would 
be easy to find analyses that would show much less. Some 
of the very important substances are present only in tenths 
or even hundredths of a percent. The great bulk of the 
soil contributes nothing to plant growth other than to furnish 
mechanical support and to store air and water for the use 
of roots. 

109. Relation of composition to productiveness. — The 
productiveness of a soil is not necessarily directly propor- 
tional to the quantity of plant-food materials that it con- 



94 



SOILS AND FERTILIZERS 



tains. This is because there are so many conditions, to 
which soils are subject, that interfere with the ability of 
plants to obtain the nutrients or that, in other ways, inter- 
fere with plant growth. It is, however, possible for the 
quantity of some substance required by plants to be so small 
that it is not sufficient to furnish enough nutriment for prof- 
itable crop production. Probably all of the soils, whose 




Fig. 20. — Relative quantities of potash, lime, phosphoric acid and nitro- 
gen in a sack containing 200 pounds of dry soil, when the percentages present 
are respectively 1.98, 1.64, 0.19 and 0.165. 

analysis is stated in Table 17, would be benefited by the 
application of some fertilizers, with the possible exception 
of the rich prairie soils. This is not because there is not 
actually enough plant-food material in the soil, but because 
it is not in a form that is available to plants. 

110. Available and unavailable plant-food materials. — 
The available plant-food materials in soils consist of those 
portions of the total supply that plants are able to secure 
in their growth. We have seen that it is necessary for all 



PLANT-FOOD MATERIALS IN SOILS 95 

substances to be in solution in order that they shall be 
absorbed by plants. Soil is not readily soluble. The natu- 
ral insolubility of soil is modified by various conditions 
of the soil itself and by the plants that grow on it. The rate 
of availability of plant nutrients is, therefore, not a constant 
quantity for any soil. A soil in good tilth will produce much 
better crops than a soil in poor tilth, which means that the 
rate of availability of its plant nutrients changes with 
the physical condition of the soil. 

The available plant-food materials are not necessarily 
proportional to the quantities of plant-food materials in a 
soil. One piece of land may contain more plant nutrients 
than another and yet be less productive. It has been shown 
that the addition of four or five volumes of quartz sand to 
one volume of a heavy, but highly productive, black* clay soil 
greatly increased the productiveness, although the conse- 
quent dilution of plant-food content reduced the potash to 
0.12 percent and the phosphoric acid to 0.03 percent. The 
mechanical condition of the soil was better after applying 
the sand. 

111. Conditions that influence availability. — It is appar- 
ent that the immediate availability of the plant-food materials 
in a soil is not so much a matter of their total quantity, as 
of favorable conditions for the decomposition of both the 
organic and the inorganic matter in the soil, and for the growth 
of plants. For this reason good tilth, good drainage, warmth, 
absence of acidity and the kind and vigor of the plants are 
factors that influence availability. When any one or more 
of these conditions is unfavorable, the availability of the 
plant nutrients may be decreased. 

While all of these conditions influence the availability 
of the plant-food materials, it still remains true that, other 
things being equal, the greater the total supply of each of 
these constituents of a soil, the greater will be the total 



96 SOILS AND FERTILIZERS 

quantity of available plant nutrients, and the greater the 
productiveness of the soil is likely to be. Hence, it is 
desirable to conserve the supplies of these substances 
and to augment them, if possible, by their judicious ap- 
plication in the form of farm manures and other fertilizing 
materials, and especially to maintain the store of organic 
matter. 

112. Water-soluble matter in soil. — Although soil is 
very slightly soluble in water, an extract of soil made with 
water contains all of the substances required by plants. 
The solution obtained by extracting a soil with water is 
probably not identical in composition or concentration with 
the solution presented to the root-hairs of plants for their 
nourishment, because the plant by the excretion of carbon 
dioxide, and possibly in other ways, aids in dissolving plant 
nutrients. It is probably true, however, that the solution 
obtained by water is the nearest approximation that we have 
to the solution presented to roots and is, for that reason, 
deserving of attention. 

113. Relation of water-soluble matter to productiveness. 
— It might be expected that there would be a direct relation 
between the productive capacity of a soil and the quantities 
of plant nutrients in its water extract, and that this relation 
would hold between different soils. This would imply that, 
as between two or more soils ; the plant-food materials dis- 
solved by water would, in general, be proportional to the 
quantities of the readily available constituents in the soil. 
It has been demonstrated that such relations do obtain 
between certain soils, but it has not been proven that this 
is invariably the case. Indeed it is probable that soils which 
differ, little in their productivity would not, in every instance, 
show such a direct proportional relationship. Experiments 
with four good and four poor soils showed the following 
averages for their crop yields and water extracts. 



PLANT-FOOD MATERIALS IN SOILS 



97 



Table 19. — Average Yields and Composition of Water Ex- 
tracts of Four Good and Four Poor Soils 



Crop Yields per Acre 

Corn, bushels 

Potatoes, bushels 

Water soluble salts in pounds per acre of surface 
four feet 

Nitrogen 

Phosphoric acid 

Potash 

Lime 

Magnesia 




Good Soils 



64.3 
213.2 



82 

192 

319 

1422 

576 



A somewhat similar result was obtained with two soils 
contained in large tanks from which drainage water was 
collected, and that have been under experiment for a num- 
ber of years. Each tank holds about three and one-half 
tons of soil. In 1915 tanks filled with soils of different types 
were planted to corn. The yields of grain and stalks com- 
bined are given in Table 20 and also the number of pounds 
to the acre of plant nutrients in drainage water collected 
during seven months from the same soil types kept bare 
of vegetation. As only a trace of phosphoric acid was found 
in the drainage that ingredient is not included in the table. 

Table 20. — Yields of Crop and Plant-Food Material in 
Drainage Water from Two Soil Types 





Soil Type 




Dunkirk 
Clay Loam 


Volusia 
Silt Loam 


Yield of corn silage (tons per acre) .... 
Substances in drainage water (lbs. per acre) 
Nitrogen 


13.4 

72 
438 

81 
100 


7.8 
59 


Lime 


360 


Magnesia 


57 


Potash 


52 







98 SOILS AND FERTILIZERS 

In this case, as in that of the four soils, previously cited, 
there is a correlation between the productiveness of the soils 
and the composition of the water extract. 

114. Chemical analysis of soil. — There have been many 
methods devised for the chemical analysis of soil. The 
important difference between these is in the solvent used 
to bring the soil into solution. Most solvents dissolve only 
a part of the soil, in which case the result of the analysis 
does not show the entire amount of all the constituents, and 
does not, therefore, show the total quantity of the plant-food 
materials in the soils. The figures given in Table 17 are 
obtained from a complete solution of the soils analyzed and 
hence show their ultimate composition. 

The advantage of an analysis of this kind is that one can 
judge of the lasting qualities of the soil, and if any particular 
constituent is present in very minute quantity that fact 
is disclosed, and measures can be taken to augment the 
supply, but nothing, however, as to immediate productive- 
ness can be learned. A collection of rocks may yield to this 
analysis as much phosphoric acid, potash, lime, or other 
nutrient, as a rich soil. Such an analysis is useful only to 
ascertain the ultimate limitations of a soil, or its possible 
deficiency in any essential constituent. 

Various solvents have been used with the intention of 
finding the quantities of food materials that plants may be 
expected to obtain in a reasonable length of time, or in other 
words to determine the available plant-food materials. 
These methods fail because availability, as we have just 
seen, depends on the conditions to which a soil is subjected 
in the field, and as these naturally vary from time to time 
it is impossible to find any one solvent that will measure 
such a variable quantity as availabilit}'. 

Chemical analyses of soil are useful in connection with 
investigations of questions relating to soils but it is not 



PLANT-FOOD MATERIALS IN SOILS 



99 



always possible, as the result of a chemical analysis, to esti- 
mate the degree of productiveness of a soil, or to say that it 
should have a certain kind of fertilizer treatment, or that it 
is adapted to certain crops. 

115. Absorptive properties of soils. — If a solution of 
certain substances required by plants be poured on soil they 
will not leach through the soil unaltered, but part will be 
held by the soil. On the other hand, the drainage water 
may contain an increased quantity of some other substance 
in place of the one added in solution. As an example of 
this we may take the following case. An application of 
200 pounds to the acre of a potash fertilizer was made 
annually for five years to soil contained in one of the large 
tanks previously referred to. The composition of the drain- 
age water from the tank so treated, and of the drainage 
water from an untreated soil is shown in the following table : 

Table 21. — Annual Average Pounds to the Acre of Lime, 
Magnesia and Potash in Drainage from Soil Treated 
with Potash Fertilizer and from Untreated Soil 





Constituents in Drainage Water 




Lime 


Magnesia 


Potash 


Potash fertilizer .... 
No fertilizer 


298 
248 


81 
56 


53 
55 



In this case the effect of the application of the potash 
fertilizer was to increase the quantities of lime and magnesia 
in the drainage water, but not the quantity of potash. 

116. Selective absorption. — Some substances are retained 
by soils only in small part. Among these are nitrates, 
which, as we shall see later, are very important forms of 
nitrogen, and sulfates, which are also required by plants. 



100 SOILS AND FERTILIZERS 

When sulfate was added annually to soil in one of the tanks 
already mentioned, for a period of five years, as much as 
two-thirds of the quantity applied was removed in the drain- 
age water, in addition to what would have been removed if 
the soil had received no sulfate. The potash previously 
mentioned as having been applied to this soil, and the sulfate 
here spoken of were one substance called sulfate of potash. 
The latter was held by the soil and the sulfate largely leached 
through. It is evident that the substance was decomposed 
in part or in whole. 

It is thus apparent that there are certain soluble fertilizers 
that may be applied to soils without much danger of loss 
by leaching and other fertilizers that are likely to be partly 
carried out of the soil in this way. 

117. The availability of absorbed fertilizers. — When a 
soluble fertilizer is absorbed by a soil, a part of it, at least, 
is held in a condition in which it is more readily available 
to plants than is the large mass of plant-food material origi- 
nally in the soil. Thus there may be in a soil several 
thousand pounds to an acre of nitrogen, phosphoric acid or 
potash in the three or four feet through which roots ramify, 
and yet the yield of crops on this soil may be materially 
increased by the application of less than a hundred pounds 
of one or more of these substances. 

The ability of soil to hold fertilizers in a readily available 
form is strikingly illustrated by an experiment at the Ptotham- 
sted Experiment Station in which soil from plats that had 
been treated with certain fertilizers for many years was 
thoroughly extracted with water and the extracts analyzed. 
Complete analyses of the soil from the several plats were 
also made. The yields of crops on these plats had been 
recorded for many years and the annual average of these, 
together with the analytical data, is given in the accompany- 
ing table : 



PLANT-FOOD MATERIALS IN SOILS 



101 



Table 22. 



Yields of Crops and Composition of Soil and 
Water Extract of Soil 





Yield 

per 
Acre 

Pounds 


Complete Analy- 
sis Percentages 


Water Extract 
Parts per Million 


Soil Treatment 


Phos- 
phoric 
acid 


Potash 


Phos- 
phoric 
acid 


Potash 


Unmanured 

Nitrogen and phosphoric 

acid 

Nitrogen and potash . 
Complete fertilizer . . 
Farm manure .... 


1,276 

3,972 

2,985 
5,087 
6,184 


0.099 

0.173 
0.102 
0.182 
0.176 


0.183 

0.248 
0.257 
0.326 
0.167 


0.525 

3.900 
0.808 
4.025 
4.463 


3.40 

3.88 
30.33 
24.03 
26.45 



It may be observed that the water extract of the soil from 
the plats treated with any fertilizer ingredient was much 
richer in that constituent than were the plats not so treated, 
while the total quantities found in the soil were not propor- 
tionately increased. 

118. Other forms of available plant-food materials in soil. 
— The natural weathering of soil that goes on continually 
makes soluble a part of the originally insoluble mineral mat- 
ter and this is absorbed just as are the fertilizer salts. When 
land is cropped each year, this soluble matter is used by 
plants about as quickly as it is formed, but when land is 
bare fallowed the dissolved matter is largely absorbed, and 
thus a bare fallow increases the quantity of available nutri- 
ents for the following crop. 

Another, and very important supply of available plant 
nutrients, is that combined with the organic matter in soils. 
When organic matter is incorporated with soil, decomposi- 
tion begins, acids are formed and these unite with mineral 
matter previously in a difficultly soluble condition. The 
result is a compound, partly organic and partly inorganic. 
These compounds decay still further until all the organic 
matter passes off as we have already seen (§ 50), and the 



102 



SOILS AND FERTILIZERS 



inorganic matter that remains is either used directly by plants 
or is absorbed in the same way as the soluble fertilizers. 

In an experiment several organic substances were mixed 
with soil, the quantities of phosphoric acid and potash com- 
bined with organic matter being determined before mix- 
ing and after standing for a year or more. The results of 
some of these experiments are given in the following table : 

Table 23. — Combinations of Phosphoric Acid and Potash 
with Organic Matter Produced by Mixing Organic 
Matter with Soil 



Experiment with cow manure and soil 

In original manure and soil . . . 

In mixture after standing .... 

Gain in organic form 

Experiment with green clover 

In original soil and clover .... 

In mixture after standing .... 

Gain in organic form 

Experiment with meat scrap 

In original soil and meat scrap . . 

In mixture after standing .... 

Gain in organic form 



Phosphoric 
Acid Grams 



1.17 
1.62 

0.45 

3.21 
3.74 

0.53 loss 

1.07 
1.18 
0.11 



Potash 
Grams 



1.06 
1.27 
0.21 

5.26 
4.93 
0.33 

0.25 
0.36 
0.11 



When the organic compounds thus formed undergo further 
decay the inorganic plant-food materials become available. 

119. Loss of plant-food material in drainage water. — 
The drainage water from cultivated fields in humid regions, 
and to a less extent in semi-arid and arid regions, except 
where irrigation is practiced, carries off very considerable 
quantities of plant-food material. When it is considered 
that soil is constantly subjected to leaching by rainwater 
passing through it, that this amounts to many tons of water 
in the course of a year on every acre of land, and that a water 
extract of soil always contains some of each of the substances 



PLANT-FOOD MATERIALS IN SOILS 



103 



required for plant growth, it is not hard to realize that there 
must result a constant and significant loss of fertility. The 
plant-food materials lost in largest quantity are lime, mag- 
nesia, potash, nitrogen and sulfur. Phosphoric acid is 
not removed in large quantity from any soil and appears 
only in traces in the drainage water of most soils. 

120. Quantities of plant-food materials in drainage. — 
The quantities of . plant-food materials that are removed 
from soil in the course of a year will depend on a variety of 
conditions and, to some extent, these and the total losses 
that may be expected are indicated by the following table, 
which is based on the annual average loss for a period of 
five years from a Dunkirk clay loam soil contained in tanks 
four feet deep and four feet two inches square. 

Table 24. — Number of Pounds of Plant-Food Materials 
Removed in Drainage Water from One Acre of Land 



Tank 

No. 


Crop 


Fertilizer 


Lime 


Mag- 
nesia 


Pot- 
ash 


Nitro- 
gen 


Sul- 
fur 


3 

4 

11 


Rotation 
No vegetation 
Rotation 


No fertilizer 

No fertilizer 

Sulfate of 

Potash 


281 
519 

298 


50 
99 

81 


64 

88 

53 


7 
102 

5 


32 

45 

56 



121. Effect of crop growth on loss of plant nutrients in 
drainage. — It will be seen that the loss of lime is very large, 
amounting to several hundred pounds to the acre. The soil 
with no vegetation has suffered much more in this respect 
than has the soil that was planted. The soil that was 
fertilized with sulfate of potash lost somewhat more lime 
than did the unfertilized soil. The loss of magnesia followed 
the same course as did the lime. More potash was lost 
from the unplanted soil than from the cropped, but the use 
of a potash fertilizer did not increase the removal of potash. 

In the case of nitrogen, the effect of not cropping the soil 



104 



SOILS AND FERTILIZERS 



is astonishing. The loss from the cropped soil is moderate, 
but from the implanted soil it is excessive. The loss of sulfur 
is decreased by cropping, and much increased by fertilizing 
with sulfate of potash. 

The loss of lime and nitrogen in the uncropped soil as 
compared with the one that w^as cropped is greater than 
the quantity that would have been removed by ordinary 
crops. Consequently there is an actual saving of these 
plant-food materials when crops are produced. 

122. Effect of fertilizers on loss of plant-food materials 
in drainage. — We have seen that the effect of sulfate of 
potash was to increase the loss of lime, magnesia and sulfur. 
In general, the result of fertilizer applications is similar to 
that shown above. This is borne out by experiments con- 
ducted at the Rothamsted Experimental Station in which 
drainage was collected from plats treated with different 
fertilizers. The total flow of drainage water from these 
plats was not measured, but the composition of the water 
indicates the effect of the fertilizers. 

Table 25. — Composition of Drainage Water from Wheat 
Plats, Rothamsted Experiment Station 



Plat 


Manures Applied, Rate 
per Acre 


Parts per Million 


No. 


Lime 


Magnesia 


Potash 


Nitrogen 


2 


Farm manure, 14 tons . 


147.4 


4.9 


5.4 


16.3 


3 and 4 


No manure 


98.1 


5.1 


1.7 


4.0 


5 


Minerals only .... 


124.3 


6.4 


5.4 


5.2 


6 


Minerals + 200 lbs. am- 












monium salts . . . 


143.9 


7.9 


4.4 


8.7 


8 


Minerals + 600 lbs. am- 












monium salts . . . 


197.3 


8.9 


2.7 


17.2 


9 


Minerals + 550 lbs. ni- 












trate of soda .... 


118.1 


5.9 


4.1 


18.6 


13 


Ammonium salts + super- 
phosphate + sulfate of 












potash 


201.4 


9.3 


3.3 


17.6 



PLANT-FOOD MATERIALS IN SOILS 105 

Without going over this table in detail, it may be noticed 
that the effect of both farm manure and commercial fertiliz- 
ers is to increase the percentage of plant-food materials in 
the drainage water. 

123. Drainage water from different soils. — The composi- 
tion of the drainage water varies with different soils. 
Table 20 in which the composition of the drainage water 
from Dunkirk clay loam and Volusia silt loam is given, is 
an illustration of the very considerable differences that 
may occur in this respect. The more productive soil has 
lost the greater quantity of plant-food material. The rates 
of loss, however, are not proportional to the amounts of 
plant nutrients that the soils contain. The Dunkirk soil 
contains less nitrogen than the Volusia, but has lost more in 
the drainage water. 

124. Absorption of food materials by plants. — It is only 
when substances are in solution that they may be absorbed 
by agricultural plants. This means that the soil from which 
plants draw their nourishment must contain water. Plants 
absorb both water and nutrient salts through their roots, 
more especialfy through the root-hairs, as these have very 
delicate walls through which solutions may readily pass. 
The movements of water and of salts through the walls of the 
root-hairs are independent of each other. When the weather 
is very hot and dry, a larger proportion of water to salts will 
pass into the roots than when the weather is cool and moist. 

125. How plants absorb nutrients. — When a solution 
of plant nutrients is brought in contact with roots, there is 
a tendency for the solution in the inside of the root and that 
on the outside to become of the same strength for each par- 
ticular substance in the solution. Thus, if there is much 
available nitrogen in the solution, it will be absorbed in 
greater quantity than if there were very little. Then, when 
the nitrogen in the plant juice is utilized by the plant to 



106 



SOILS AND FERTILIZERS 



form tissue, it is removed from the juice and more nitrogen 
is absorbed to reestablish equilibrium. 

The substances that are used by plants in large amounts 
are absorbed in greater quantity than those that are not 
required in making tissue, or in other ways removed from 
solution in the plant juices. The unused substances that 
remain in the plant juices prevent, by their presence, the 
further absorption of those particular substances from the 
soil water. It is important that substances like nitrogen, 
phosphoric acid, potash and lime shaft be present in abundant 
quantities in the solution from which crops draw their 
nourishment. 

126. How roots aid in solution of soil. — In addition to 
their function in the absorption of plant nutrients, there 
can be no doubt that roots aid in the solution of these nutri- 
ents from the soil. One way is by the excretion of carbon 
dioxide, which when dissolved in water is an excellent solvent 
for such substances as lime, potash and even phosphoric 
acid when present in certain forms. The following table 
shows the percentage of carbon dioxide in air drawn from 
the bottom of the large soil tanks that have previously been 
mentioned. One of these tanks produced a crop of corn 
during the summer when the analyses were made, the other 
tank was kept bare of vegetation. 

Table 26. — Percentage of Carbon Dioxide in Air of Soil 
Planted to Corn and of Bare Soil 



Date op Analysis 


Planted Soil 


Unplanted Soil 


Difference 


Aug. 19 ... . 
Aug. 23 ... . 
Aug. 26 ... . 
Aug. 30 ... . 
Sept. 2 . . . . 


3.42 
3.53 
3.44 
3.03 
3.28 


2.45 
2.00 
2.37 
2.04 
2.17 


.97 
1.53 
1.07 

.99 
1.11 



PLANT-FOOD MATERIALS IN SOILS 107 

It is apparent that the effect of the growth of plants has 
been to increase the amount of carbon dioxide in the soil 
air. The figures represent the period of the greatest pro- 
duction of carbon dioxide by the corn plant. 

127. Production of carbon dioxide by microorganisms. 
— In addition to the carbon dioxide excreted from roots, 
there are large quantities produced by microorganisms that 
exist in soils. These organisms are concerned in the decom- 
position of organic matter, and one final product of such 
action is carbon dioxide. It has been estimated that in 
one acre of soil to a depth of sixteen inches, there are sixty- 
eight pounds of carbon dioxide produced by bacteria and 
fifty-four pounds excreted by roots during the growing 
season. 

128. Solvent action of roots in other ways. — Many in- 
vestigators think that the large quantities of mineral matter 
that plants remove from soils could not be obtained from 
the water solution even with the aid of carbon dioxide. 
Several different ways have been suggested by which plants 
may assist in rendering soluble the nutrients contained 
in soils. It will not be necessary to discuss these as there 
has been no definite and conclusive outcome to the investi- 
gation of the subject. The indications are, however, very 
strong that the plant aids in obtaining its food material in 
some way or ways other than by the excretion of carbon 
dioxide. 

129. Difference in absorptive power of crops. — Crops 
differ greatly in their ability to draw nourishment from the 
soil. The difference between the quantities of nitrogen, 
phosphoric acid and potash taken up by a corn crop of 
average size and a wheat crop of average size is very 
striking. In Table 27 it may be seen that two tons of 
red clover contain three times as much potash, nearly ten 
times as much lime, and somewhat more phosphoric acid 



108 SOILS AND FERTILIZERS 

than does a crop of thirty bushels of wheat, including the 
straw. 

The ability of any kind of plant to secure nutriment from 
the soil depends on a number of factors which need not be 
discussed here. According to their ability in this direction, 
plants have been popularly classified as " weak feeders " 
and " strong feeders.'' To the former belong such crops 
as wheat and onions, which require very careful soil prep- 
aration and manuring. In the latter class are maize, 
oats and cabbage which demand relatively less care. In 
the manuring and rotating of crops, this difference in ability 
to obtain nutriment must be considered, in order not only 
to secure the maximum effect on the crop manured, but 
also to get the greatest residual effect of the manure on suc- 
ceeding crops. 

130. Substances needed by plants and substances merely 
absorbed. — Some substances found in soils and absorbed 
by plants are used for the formation of plant tissue, and 
hence are indispensable. Other soil constituents, although 
absorbed by plants to sufficient extent to be found in their 
ash, are not essential to a normal growth of crops. The 
substances that are essential are generally present in plants 
in considerable quantities, because they constitute a part 
of the plant tissue. 

131. Quantities of plant-food materials removed by crops. 
— When crops are removed from the land, they carry in 
their tissues considerable quantities of plant-food materials. 
The drain on the total supply may be serious if the soil is 
not well supplied with these substances. The larger the 
yield of crops the greater the quantities of plant nutrients 
they are likely to contain. The following table shows the 
quantities of nitrogen, potash , phosphoric acid and lime 
removed from an acre of land by some of the common crops. 
The entire harvested crop is included : 



PLANT-FOOD MATERIALS IN SOILS 



109 



Table 27. — Number of Pounds of Nitrogen, Potash, Lime 
and Phosphoric Acid Removed from One Acre of Soil by 
Certain Crops 



Crop 


Yield 


Nitrogen 


Potash 


Lime 


Phosphoric 
Acid 


Wheat . . . 


30 bushels 


48 


28.8 


9.2 


21.1 


Barley . . . 


40 bushels 


48 


35.7 


9.2 


20.7 


Oats .... 


45 bushels 


55 


46.1 


11.6 


19.4 


Corn .... 


30 bushels 


43 


36.3 


— 


18.0 


Meadow hay . 


1^ tons 


49 


50.9 


32.1 


12.3 


Red clover 


2 tons 


102 


83.4 


90.1 


24.9 


Potatoes . . 


6 tons 


47 


76.5 


3.4 


21.5 


Turnips . . . 


17 tons 


192 


148.8 


74.0 


33.1 



While these are only a few of the cultivated crops, they 
give some idea of the quantities of plant-food materials 
removed from soils by ordinary cropping. The nitrogen 
removed by red clover is partly taken from the air and conse- 
quently the draft on the soil supply is not so great as would 
be indicated by the figure here given. 

132. Possible exhaustion of mineral nutrients. — Com- 
paring the figures given above with those in Table 17 
it is evident that there is a supply in most arable soils 
that will afford nutriment for average crops for a very long 
period of time. On the other hand, when it is considered 
that the soil must be depended on to furnish food for hu- 
manity and domestic animals as long as they shall continue 
to inhabit the earth, at least so far as is now known, the 
very apparent possibility of exhausting, even in a period 
of several hundred years, the supply of plant nutrients 
becomes a matter of grave concern. 

The visible sources of suppty to replace or to supplement 
the nutrients in the soil now cultivated are, for the mineral 
substances, the subsoil and the natural deposits of phosphates, 
potash salts and limestone ; and for nitrogen, deposits of 
nitrates, the by-product of coal distillation and the nitrogen 



110 SOILS AND FERTILIZERS 

of the atmosphere. The last of these is inexhaustible, 
and the exhaustion of the soil nitrogen supply, which a few 
years ago was thought by some to be a matter of less than 
half a century, has now ceased to cause any apprehension. 
The conservation or extension of the supply of mineral 
nutrients is now of supreme importance. The utilization 
of city refuse and the discovery of new mineral deposits 
are developments well within the range of possibility, but 
neither of these promises to afford more than partial relief. 
The utilization of the subsoil through the gradual removal 
by natural agencies of the topsoil will, without doubt, tend 
to constantly renew the supply. The removal of topsoil 
by wind and erosion is, even on level land, a very considerable 
factor. The large amount of sediment carried in streams im- 
mediately after a rain, especially in summer, gives some idea of 
the extent of this shifting. This affects chiefly the surface soil, 
and thereby brings the subsoil into the range of root action. 
There is little doubt that a moderate supply of plant- 
food materials will always be available in most soils, but for 
progressive agriculture manures must be used. 

QUESTIONS 

1. How does the total quantity of plant-food materials in soils 
compare with the total weight of soil ? 

2. Are the percentages of nitrogen, phosphoric acid and potash 
uniform in different soils, or do they differ ? 

3. Is there a direct relation between the productiveness of a soil 
and its content of plant-food materials ? 

4. What is meant by available and unavailable plant nutrients ? 

5. Name some of the factors that influence the availability of 
plant nutrients in soils. 

6. Why is it not always possible to determine by chemical analy- 
sis the degree of productiveness of a soil ? 

7. Explain what is meant by the absorptive properties of soil for 
soluble fertilizers. 

8. Explain what is meant by selective absorption. 



PLANT-FOOD MATERIALS IN SOILS 111 

9. Explain the availability of absorbed fertilizers. 

10. What two constituents are removed in greatest quantity 
by drainage water from an unplanted soil ? 

11. Explain how roots aid in the solution of soil. 

LABORATORY. EXERCISES 

Exercise I. — Soluble matter of soil. 

Materials. — A very rich soil, filter paper and funnel, evaporat- 
ing dish, flame, dilute hydrochloric acid. 

Procedure. — Place a small amount of a rich soil on a filter paper 
held in a funnel and leach with distilled water, catching percolate 
in an evaporating dish. Evaporate percolate to dryness and exam- 
ine residue. Is it large or small in amount ? Treat with a few 
drops of dilute acid. Finally heat over a flame. Explain results. 
This soluble matter is the most valuable portion of the soil. 

Exercise II. — Absorptive power of soil for dyes. 

Materials. — Soil, filter paper, funnel, solution of gentian violet. 

Procedure. — Place a small amount of soil on a filter paper in a fun- 
nel and treat with a solution of gentian violet. Note that the water 
comes through clear for a considerable period indicating the high ab- 
sorptive power of the soil for this dye. The capacity of the soil to 
absorb soluble matter prevents heavy losses of plant-food materials. 

Exercise III. — Selective absorption by the soil. 

Materials. — Soil, filter paper and funnel, solution of gentian 
violet and solution of eosin. 

Procedure. — Proceed in the same way as Exercise II, comparing 
the absorptive power of portions of the same soil for the two dyes. 
Note the difference. The soil varies in its absorptive power with 
different materials. For instance, the soil absorbs acid phosphate 
much more strongly than sodium nitrate. 

Exercise IV. — Absorptive power of the soil for gas. 

Materials. — A moist loam rich in organic matter, a flask or 
bottle, concentrated ammonia. 

Procedure. — Place in a flask or bottle a quantity of moist soil. 
Pour in a few drops of ammonia. Note strong odor. Stopper 
bottle and shake. Allow to stand for half an hour with several shak- 
ings. Open and note odor. 

The absorptive power of the soil for ammonia, oxygen and other 
gases is a very important function. Explain why this is true. 



CHAPTER VIII 
ACID SOILS AND ALKALI SOILS 

Some soils are termed acid, or sour soils. They are so 
called because they give the same tests with certain chemi- 
cals that are obtained with vinegar and other acids. A 
common test for acids is to bring them in contact with blue 
litmus paper, and if the material is acid the paper is colored 
red. Soils that are strongly acid will also do this. Another 
property of acid materials is that, if sufficient quick-lime 
is brought in contact with them they will no longer color 
blue litmus paper red. This may be tried by slowly stirring 
quick-lime into vinegar and testing it occasionally with 
litmus paper. If sufficient quick-lime be added to an acid 
soil, it will no longer turn blue litmus paper red. 

Whether a soil is acid or not is a matter of practical im- 
portance, because some plants do not grow so well on sour 
soils as they do on soils that are neutral or alkaline ; on the 
other hand some crops prefer an acid soil. 

133. Nature of soil acidity. — There are two kinds of 
soil acidity (1) when acids are present that have been formed 
by fermentation of organic matter in the soil, (2) when there 
is a deficiency of such material as lime or potash. In either 
case the soil will color blue litmus paper red. 

134. Positive acidity. — The condition of soil first men- 
tioned above has been termed positive acidity. It arises 
from the decomposition of organic matter when soil condi- 
tions are not favorable to the proper breaking down of the 
intermediate substances. An insufficient air supply caused 

112 



ACID SOILS AND ALKALI SOILS 113 

by saturation or compaction of the soil, or a lack of lime, may 
lead to the formation of these acids. Acid soils to which 
certain organic acids have been added were found to be 
unfavorable to the growth of plants like wheat, while the 
same soil, to which lime had been applied, produced a much 
better growth. Lime overcomes the injurious effect of this 
kind of acidity. 

135. Negative acidity. — When a soil contains no free 
acids but is sour in its relations to plant growth, it may be 
said to possess negative acidity. Negative acidity is coun- 
teracted by the application of lime just as is positive acidity. 
The condition that renders the soil acid is a lack of sub- 
stances like lime, magnesia, soda and potash. Any one of 
these four substances is called a base. Lime, being the cheap- 
est of these to apply, is the usual corrective. The injurious 
action of soil acidity on plant growth has been attributed 
to one or more of the following causes : (1) lack of lime to 
overcome organic acids when they are formed ; (2) absence 
of sufficient carbonate of lime ; (3) great absorbent properties 
that cause the soil to compete with plants in their attempt 
to draw plant-food materials from the soil. 

136. Ways by which soils become sour. — In regions of 
ample rainfall there is always a tendency for soils to become 
sour, and unless they originally contain large quantities 
of lime, or are of recent formation, they are likely to be in 
need of lime. This tendency may be due to any one or more 
of the following causes : (1) removal of lime and similar 
substances in drainage water; (2) removal of these sub- 
stances by plants ; (3) accumulation of acids contained in 
fertilizers applied to the soil ; (4) formation of organic acids 
from plant remains. 

137. Drainage as a cause of acidity. — The chief cause of 
soil acidity is doubtless the removal of lime, magnesia, soda 
and potash from soil by the water that percolates through 



114 SOILS AND FERTILIZERS 

the soil and passes off as drainage. The quantities of these 
materials that are annually lost from an acre of soil, as found 
by lysimeter experiments, are shown in Table 24. 

It will be noticed that there is a much greater loss from the 
unplanted soil than from the planted. The quantities of 
these materials taken up by some crops is much less than the 
difference between the quantities in the drainage in the 
planted and unplanted soil, hence the growth of these crops 
on land is really a means of saving lime. 

138. Effect of plant growth on soil acidity. — Plant growth 
may promote soil acidity in the following ways : (1) by re- 
moval of the bases in the ash of the plants ; (2) by leaving 
in the soil the acids with which these bases were combined ; 
(3) by formation of organic acids during decomposition of 
plant remains. 

It will be seen from Table 27 that the quantities of 
potash and lime removed in crops of average size vary 
considerably and in some cases are very large. When, 
as in a state of nature, the vegetation on the land is returned 
to it after life ceases, and its organic material is again 
incorporated with the soil, there is no loss in this way, but 
in ordinary farming most of the above ground portion of 
the crop is removed from the land. The manure of growing- 
animals returns to the soil only a small proportion of the 
lime that was originally in the plants because the animal 
has used it, and the potash is likely to be leached from the 
manure unless it is carefully handled. 

Crops in growing remove more potash and other bases 
from the soil than they do the acid-producing substances, 
which latter are left in the soil and contribute still more to 
its tendency to assume an # acid condition. 

139. Effect of fertilizers on soil acidity. — It has been 
shown very conclusively that the continued use of considerable 
quantities of sulfate of ammonia on land may result in bring- 



ACID SOILS AND ALKALI SOILS 115 

ing about an acid condition. In the case of this fertilizer 
the ammonia is absorbed either directly or indirectly and 
most of the sulfate, which is an acid, remains in the soil. 
Probably no other fertilizer is so active in producing acidity, 
but it is possible that sulfate of potash or muriate of potash 
or gypsum may, in less degree, have the same tendency. 

The use of free sulfur for combating fungous diseases may 
also lead to the formation of a sour soil. 

140. Effect of green-manures on acidity. — In soils defi- 
cient in lime the incorporation of green-manure crops has 
been thought to produce temporarily an acid condition. 
It is during the early stages of fermentation in the soil that 
the acids are formed. When further decomposition pro- 
ceeds, the acids are broken up and acidity disappears. This 
condition has been noticed mainly in the South Atlantic 
states. Where it has been found to occur, there is some ad- 
vantage to be gained from plowing under the green-manure 
as long as possible before planting the next crop. 

141. Weeds that flourish on sour soils. — Whether a soil 
is acid or not will make a great difference in the kinds of 
plants that will thrive on it. Certain weeds will generally 
be found growing on sour soil and the presence of these in 
large numbers may be taken as evidence that the soil needs 
lime. Wheels that appear to nourish on acid soils may do 
so either because they are physiologically adapted to an 
acid condition, or because other vegetation does not thrive, 
and hence these particular weeds have less competition on 
this soil. The weeds that in one part of the country or 
another may be considered to indicate an acid soil are as 
follows : 

Sheep sorrel Corn spurry 

Paintbrush Wood horsetail 

Daisy Plantain 

Horsetail rush Goose-grass 



116 



SOILS AND FERTILIZERS 



142. Crops adapted to sour soils. — There are a consider- 
able number of plants, other than weeds, that grow well on 
sour soils, some, in fact, thriving better when the soil is 
acid than when it is not so. The following is a list of those 
that have been found to be adapted to soils of this kind : 



Blueberry 


Rhode Island bent-grass 


Rye 


Cranberry 


Cowpea 


Millet 


Strawberry 


Soy bean 


Buckwheat 


Blackberry 


Castor bean 


Carrot 


Raspberry 


Hairy vetch 


Lupine 


Watermelon 


Crimson clover 


Serradella 


Turnip 


Potato 


Radish 


Redtop 


Sweet potato 


Velvet bean 



This list affords a sufficient number of plants to permit of 
a largely diversified cropping system on sour soil, should it 
be undesirable, or very expensive, to put lime on the land. 
The considerable number of legumes in the list would admit 
of soil improvement through their use. 

143. Crops that are injured by acid soils. — While there 
is a considerable number of agricultural plants that are 
adapted to sour soil, it is true that the greater number of 
the most important crops is injured by such soil. General 
farming can best be conducted on soil that is not greatly 
in need of lime. One reason for this is that the great soil- 
improving crops — red clover and alfalfa — are very un- 
certain crops on acid soils. The following plants are injured 
by sour soil : 



Alfalfa 


Pumpkin 


Cucumber 


Red clover 


Salsify 


Lettuce 


Saltbush 


Spinach 


Onion 


Timothy 


Red beet 


Peanut 


Blue-grass 


Sorghum 


Okra 



ACID SOILS AND ALKALI SOILS 117 



Maize 


Barley 


Tobacco 


Oats 


Sugar beet 


Kohlrabi 


Pepper 


Currant 


Eggplant 


Parsnip 


Celery 


Mangel-wurzel 


Cauliflower 


Cabbage 





Some of these plants will grow well on soil that is too sour 
for other crops. For example, red clover will grow fairly 
well on soil that is too acid to raise alfalfa. 

144. Litmus paper test for soil acidity. — This test is 
made with blue litmus paper, which is brought in imme- 
diate contact with wet soil. A rapid and decided change 
to red is taken to indicate an acid condition of the soil. 
Carbonic acid, which is always present in soils, but 
which is not injurious to plant growth, is supposed to give 
only a faint pink color to the litmus paper. Various ways 
of bringing the paper into contact with the soil have 
been proposed, among others the placing of filter paper or 
blotting paper between the soil and the litmus paper. 
It has also been pointed out that the acid perspiration of 
the fingers may lead to a mistaken conclusion that the soil 
is acid. 

Much litmus paper is sold that is of very poor quality, 
and an effort should be made to obtain a good article. When 
good paper is used and the test is carefully made, the general 
experience has been that it is a fairly good, although not an 
infallible, guide to the need of a soil for lime. 

145. Litmus paper and potassium nitrate. — This is per- 
formed in the same manner as the former litmus paper test, 
except for the substitution of a saturated solution of potas- 
sium nitrate instead of water for moistening the soil. It is 
a more delicate test than the one with litmus paper alone. 
The operation consists in working a small soil sample to a 
thick paste with a saturated solution of potassium nitrate 



118 SOILS AND FERTILIZERS 

and applying the paper directly to the soil. If the soil is 
acid, the potassium will be absorbed and an acid or acid salt 
set free, which will act on the litmus paper, giving it a decided 
pink color. 

146. The Truog test. — In this test solutions of calcium 
chloride and zinc sulfide are brought in contact with the 
soil to be tested and the mixture is boiled. If the soil is 
acid, a gas called hydrogen sulfide is formed and driven off 
with the steam. The presence of this gas may be detected 
by placing a strip of moist lead acetate paper over the mouth 
of the flask in which the soil and solutions are boiled. The 
lead acetate paper is rapidly darkened by the hydrogen 
sulfide gas as it passes out of the flask. Detailed descrip- 
tions of the methods for making these tests for soil acidity 
will be found in the laboratory exercises. 

147. Alkali soils. — We have seen that every soil is 
constantly undergoing decomposition, by which process a 
very minute fraction becomes soluble every year. Ordi- 
narily, in humid regions, this soluble matter is leached out 
by the rain water that percolates through the soil. In 
those parts of the world where the rainfall is very slight, 
and yet where decomposition of soil proceeds, there is a 
tendency for the soluble matter to accumulate in the soil 
where there is no drainage, or for it to move to places where 
seepage accumulates. A strong accumulation of such soluble 
matter is known as alkali because it usually has an alkaline 
reaction, i.e. it turns red litmus paper blue. 

148. Nature and movements of alkali. — Because of its 
easy solubility, alkali may move from place to place or up- 
ward and downward in soils. During periods of drought 
it is carried upward by the capillary rise of the soil water, 
while during periods of rainfall it may move downward, 
where it is out of range of roots. The composition of alkali 
varies greatly in different regions. The main distinctions 



ACID SOILS AND ALKALI SOILS 119 

are between white and black alkali. The former gets its 
name from the fact that when it accumulates on the surface 
of the ground, as is very common in a dry time, it has a white 
appearance. The latter, on the other hand, is black, because, 
owing to its caustic nature, it dissolves organic matter from 
the soil, which gives it a black color. 

149. Effect of alkali on crops. — Both white and black 
alkalis are injurious to plant growth when present in large 
quantity, but black alkali is much more active in this re- 
spect, as it attacks plant tissue just as it does the organic 
matter in soils. White alkali injures plants by withdraw- 
ing water from the plant cells and causing the plant to 
wilt. The nature of the salts contained in the alkali, and 
the species and even the individuality of the plant, de- 
termine the amount of alkali that is required to destroy a 
crop. 

150. Tolerance of different plants to alkali. — Some plants 
are better able to endure the presence of alkali in soil than 
are others. This is due, in part, to the natural resistance 
of the plant to the injurious effect, and in part to the rooting 
habit of the plant. Deep-rooted plants are, in general, 
better able to resist alkali than are shallow-rooted ones, 
probably because some part of the root is in a less strongly 
impregnated part of the soil. 

Of the cereals, barley and oats are the most tolerant. Of 
the forage crops, a number of valuable grasses are able 
to grow on soil containing a considerable quantity of 
white alkali. Timothy, smooth brome-grass and alfalfa 
are among the cultivated forage crops most tolerant of 
alkali, although they do not equal the native grasses in this 
respect. 

The resistance of a number of plants to white alkali, ex- 
pressed in pounds to the acre to a depth of four feet, is as 
follows : 



120 SOILS AND FERTILIZERS 

Table 28. — Resistance of Crops to Alkali 



Crop 


Total Alkali 


Crop 


Total Alkali 


Peaches . . . 


11,280 


Barley . . . 


25,520 


Rye .... 


12,480 


Grapes . . . 


45,760 


Apples . . . 


16,120 


Sugar beets 


59,840 


Pears .... 


20,920 


Sorghum . . 


81,360 


Oranges . . . 


21,840 


Alfalfa . . . 


110,320 






Saltbush . . 


156,720 



151. Irrigation and alkali. — Frequently the injurious 
presence of alkali in an irrigated region has been discovered 
only after irrigation has been practiced for a number of years. 
This is due to what is termed " rise of alkali," and comes 
about through the accumulation, near the surface of the 
soil, of salts that were formerly distributed throughout 
a depth of perhaps many feet. Before the land was irrigated, 
the alkali was distributed through a great depth of soil, but 
after water was turned on, this was dissolved, and later 
brought .to the surface, as the soil was allowed to dry out. 
The upward movement in such cases exceeds the downward 
because the descending water passes largely through the 
non-capillary pore spaces, while the ascending water passes 
entirely through the capillary spaces. The alkali accumu- 
lates principally in the capillary spaces and hence is swept 
to the surface in large quantities by the upward movement 
of capillary water. 

152. Removal of alkali. — There are several ways in 
which alkali may be removed from soil, among which are 
the following : (1) leaching with underdrainage ; (2) correc- 
tion with gypsum ; (3) scraping ; (4) flushing. 

The first of these consists in laying tile drains, much as is 
done for draining land in humid regions, then flooding the 
land with large quantities of water, which dissolves the alkali 



ACID SOILS AND ALKALI SOILS 121 

and carries it out through the drains. This is, by all means, 
the most effective way of removing alkali. 

Gypsum has been used for converting black alkali into 
white alkali, which it does by inducing chemical changes in 
the alkali. This may well be used when black alkali land 
is to be drained. 

Scraping consists in allowing alkali to accumulate at the 
surface of the soil and then removing it with a scraper. This 
is never a very effective treatment. 

Flushing is accomplished by removing the surface incrusta- 
tion with a rapidly moving stream of water instead of a 
scraper. Tike the former method it is not usually an 
adequate treatment. 

153. Control of alkali. — Instead of actually removing 
alkali its injurious action may often be kept in check by keep- 
ing it well distributed through the soil and not allowing it 
to accumulate near the surface. This may be done by con- 
trolling evaporation and by the cultivation of alkali-tolerant 
plants. The methods usually employed for retarding evap- 
oration of moisture are generally applicable for controlling 
alkali. 

Cropping with alkali-tolerant plants naturally suggests 
itself as a means of combating alkali where it does not exist 
to such an extent as to interfere with all crop production. 
As these plants remove considerable quantities of alkali in 
their ash, they also serve as a means of alkali removal. 

QUESTIONS 

1. Distinguish between positive and negative acidity in soils. 

2. Describe three ways in which soil acidity may be injurious to 
plant growth. 

3. State three ways by which the growth of plants on soil tends 
to make it become sour. 

4. What is the effect on soil acidity of a continued use of am- 
monium sulfate ? 



122 SOILS AND FERTILIZERS 

5. If green-manures are found to produce acidity on a particular 
soil, what precaution should be taken in using them ? 

6. Name three or four weeds whose presence in large numbers 
indicates that a soil is acid. 

7. Name six or eight crops that are adapted to growth on sour 
soils, and an equal number that are injured by a sour soil. 

8. Describe the litmus paper test for the detection of a sour soil. 

9. Describe the test with litmus paper and potassium nitrate 
solution. 

10. State what is meant by an alkali soil. 

11. Explain the difference between white and black alkali, and 
the effect of each on crops. 

12. Name some of the crops most tolerant of alkali. 

13. Describe four ways by which alkali may be removed from soil. 

LABORATORY EXERCISES 

Exercise I. — Acid soils in the field. 

Plan a field trip to a soil known to be distinctly acid. Observe 
structure of soil, organic content, character of crop and, particularly, 
character of other vegetation. It might be well to make a collec- 
tion of the plants which are supposed to indicate acidity. Take 
samples of this soil for future tests for acidity in the laboratory. 

Exercise II. — Litmus paper with and without potassium ni- 
trate. 

Materials. — Litmus paper, acid soil, evaporating dish, a neutral 
potassium nitrate solution. 

To prepare litmus paper boil litmus powder (1 part) with alcohol 
(2 parts) for five minutes. Allow to settle and pour off the alcohol, 
thus carrying away certain dyes of low sensitiveness. To the 
powder now add five parts of water. Boil 10 minutes and allow 
to stand overnight. Decant liquid and filter it. This gets rid of 
most of the carbonates. Now make acid with sulfuric acid and bring 
back to required tint with barium hydrate. Dip narrow strips of 
filter paper into the solution and dry on glass. When dry cut into 
strips of the required size. 

Procedure. — Mix one portion of a distinctly acid soil to a thick 
paste in an evaporating dish with distilled or rain water. Allow 
to stand for a few minutes, then pat to a smooth surface and apply 
to it one end of a strip of litmus paper, leaving the other end free for 
comparison. Press paper closely in contact with soil. 




ACID SOILS AND ALKALI SOILS 123 

Treat another small portion of this soil in the same way, using 
a neutral potassium nitrate solution instead of distilled water. 

Observe the rate of change of color of the litmus paper with and 
without potassium ni- 
trate. 

Exercise III. — 
Litmus paper test.' 

Materials. — Same 
as Exercise II. 

Procedure. — Test 
a number of different Fig. 21. — Procedure in the litmus paper test. 
soils. The students («) small evaporating dish, (b) soil worked to a 
should be encouraged ^ m paste with pure water or a neutral potassium 

, . . . , . nitrate solution, (c) the litmus paper in position, 

to bring m their own with one end free for comparison, 
samples. Note whether 

there appears to be a difference in degree of acidity of these soils 
as indicated by the quickness with which the litmus paper turns red 
and the shade of red produced. 

Exercise IV. — Test for soil carbonates. 

Materials. — Soil, evaporating dish, dilute hydrochloric acid. 

Procedure. — Treat a small portion of the soil to be tested with 
dilute hydrochloric acid. Effervescence indicates the presence of 
carbonates. A soil so reacting needs no lime. If no reaction oc- 
curs, test with litmus paper, as the soil may be alkaline, neutral 
or acid. 

Exercise V. — Ammonia test for acidity. 

Materials. — Soil, 8 oz. bottle, concentrated ammonia. 

Procedure. — Place about 25 grams of soil in an 8 oz. bottle and 
add 10 c.c. of ammonia. Fill two-thirds full with distilled or rain 
water. Shake well and allow to stand overnight. A darkening 
of the supernatant liquid is an indication of the lack of lime. 

This method is not a quantitative one because the degree of 
darkening of the liquid depends on the amount of organic matter 
present rather than the degree of acidity. 

Exercise VI. — Zinc sulfide test for acidity. (See Fig. 22.) 

Materials. — Soil, 250 to 300 c.c. Erlenmeyer flask, tripod and 
wire gauze, flame, calcium chloride-zinc sulfide solution, lead ace- 
tate paper. 

The calcium chloride-zinc sulfide reagent is made up as follows : 
50 grams of neutral calcium chloride plus 5 grams of zinc sulfide 



124 



SOILS AND FERTILIZERS 



is added to 250 c.c. of distilled water. The solution should be 

shaken well each time before using as the zinc sulfide is insoluble and 

tends to sink to the bottom of the vessel. 

The lead acetate paper is made by dipping strips of filter paper 

into a saturated solution of lead acetate and drying. 

Procedure. — Place in a 250 or 300 c.c. 
Erlenmeyer flask a 10 gram sample (well 
pulverized) of the soil to be tested. Now 
add 5 c.c. of the calcium chlo ide-zinc sulfide 
reagent, the former being in solution and 
the latter in suspension. Add 75 c.c. of dis- 
tilled water. Place on a wire gauze over a 
flame and bring to boiling. Boil exactly one 
minute, being careful not to allow the sample 
to froth over. 

The boiling having become constant and 
the C0 2 being driven off, lay over the mouth 
of the flask a strip of lead acetate paper 
moistened in distilled water. Allow it to 
remain there exactly three minutes. The test 
is now complete and acidity is indicated by 
the blackening of the paper. 

Exercise VII. — Incrustation of " al- 
kali " by capillary action. 

Materials. — Sandy loam, lamp chimney, 
pan, salt. 

Procedure. — Prepare a lamp chimney by 
neatly tying over the end two thicknesses of 
cheesecloth. Fill with sandy loam. Set the 
chimney now prepared into a solution of common salt. The salt 
solution will soon rise through the column by capillary action and 
evaporation will take place from the soil. This will soon cause 
an incrustation of " white alkali " on the surface of the soil. 

Explain this experiment in relation to irrigation practice and 
moisture conservation under arid conditions. 




Fig. 22. — Apparatus 
for the zinc sulfide test 
for soil acidity, (a) lead 
acetate paper in posi- 
tion, (b) flask, (c) soil 
treated with calcium 
chloride and zinc sulfide, 
(d) tripod, (e) Bunsen 
burner. 



CHAPTER IX 
THE GERM LIFE OF THE SOIL 

Thus far we have been engaged in considering soil as 
lifeless material, on which plants are to be grown, but which 
in itself is inert and inanimate. Such a conception of soil 
is inadequate, for there is to be found in all arable land a 
vast number of forms of microscopic life that realty consti- 
tute a part of the soil itself. From the standpoint of crop 
production they are of great importance, as we probably 
should not be able to maintain soil fertility without them. 

Under germ life, as used in this chapter, are included 
bacteria, fungi, algse, and some of the molds, but we shall in 
the main, dispense with these distinctions and use the term 
" germs " or " microorganisms " to cover all or any of them. 
In spite of what has just been said about the importance of 
germs in plant production, there are many that are injurious 
to plants both directly in the causation of disease, or indi- 
rectly by contributing to processes in soils that are detri- 
mental to the conditions favorable to plant growth. In dis- 
cussing the subject it will be convenient to take up first 
the soil germs that are directly injurious to plants. After 
that the subject will be discussed according to the processes 
in the soil with which microorganisms are concerned. 

154. Microorganisms injurious to crops. — The soil germs 
that injure crops do so by attacking the roots. Those that 
attack other parts of plants may live in the soil during their 
spore stage but they are not strictly microorganisms of the 
soil. Some of the more common diseases produced by soil 

125 



126 SOILS AND FERTILIZERS 

germs are : wilt of cotton, cowpeas, watermelon, flax, tobacco, 
tomatoes, and other plants ; damping-off of a large number 
of plants, root-rot and galls. 

Some of the germs causing these diseases may live in the 
soil for many, years. Some of them will die within a few 
years if the plants on whose roots they live are not grown on 
the soil, but others are able to maintain existence on almost 
any organic substance. Infection is carried in the soil, or by 
the roots of the plants themselves, consequently farm imple- 
ments or manure may often be a means of spreading the germs. 

For combating the difficulties caused by the germs, many 
methods have been tried with more or less success. Rota- 
tion of crops is successful in some cases, but in others entire 
discontinuance is the only remedy. The use of lime has been 
beneficial in the case of some diseases. Steam sterilization 
for greenhouse soils will hold in check a considerable number 
of diseases. Strains of cowpeas and cotton plants have been 
bred that are immune to the effects produced by some germs. 

155. Germs not directly injurious to crops. — The part 
played by the microorganisms that affect the growth of 
crops may be roughly listed as follows : (1) action on mineral 
matter; (2) decomposition of non-nitrogenous organic 
matter ; (3) decomposition of nitrogenous organic matter ; 
(4) fixation of nitrogen from the air and its incorporation 
in the soil. Most of the processes involved in these trans- 
formations bring about conditions favorable to crop growth, 
but some of them are injurious, as, for instance, the forma- 
tion of substances poisonous to plants and the liberation 
of nitrogen which escapes into the air. These injuries are, 
however, not direct effects of the germs on the crops, but 
indirect ones caused by the products of the organisms. 

Bacteria, fungi, algse and certain molds all play a part 
in these processes, but none of them so actively as do the 
bacteria. On account of the dominant part that bacteria 



THE GERM LIFE OF THE SOIL 



127 



take in soil fertility some further description of their oc- 
currence in soils will be given. 

156. Numbers of bacteria in soils. — It is naturally to 
be expected that soils differ greatly in the number of bac- 
teria that they possess. Where there is a large amount of 
easily decomposable organic matter, the number is great, 
and consequently in rich garden soils that have been heavily 
manured, or where the carcasses of animals have been buried 
the bacterial flora is dense. On the other hand, in very 
sandy soils, desert soils and water-logged soils, bacteria are 
few in number. 

While there are usually many bacteria in fertile soil, it is 
not always the case that there are more in such soils than 
in less productive ones. The number of bacteria that a 
soil may contain cannot be considered a measure of its pro- 
ductiveness. The numbers of bacteria found in one gram 
of soil of different kinds and treated in different ways are 
given in the following table : 



Table 29. 



- Number of Bacteria to a Gram of Soil During 
Some Period of the Growing Season 



Soil 


Depth . 


Crop 


Number op 
Bacteria 


Stiff clay .... 


3 inches 


Orchard in high 
state of cultiva- 
tion. In cover 


2,200,000 


Adjoining soil above 
and of same char- 


3 inches 


crops 
Meadow for twelve 
years 


450,000 


acter 








Of same type as 

above .... 

Same type as above 


3 inches 


Vegetables and 
heavily manured 

Scarlet clover 
plowed under and 
alternated with 
maize for ten years 


1,800,000 
3,360,000 



128 



SOILS AND FERTILIZERS 




157. Conditions affecting bacterial growth. — The en- 
vironment is a controlling influence in the development of 
bacteria as it is of all organisms. Among the important 
environmental influences are the supply of air and moisture, 
the temperature, the presence of organic matter, and the 

presence or absence of 
acidity in the soil. 

158. Air supply. — 
While all bacteria require 
some air for their growth, 
certain of them are able 
to get along with much 
less than others. Those 
requiring an abundant 
supply of air have been 
called aerobic bacteria 
and those that thrive 
better on a small air sup- 
ply are termed anaerobic. 
The bacteria that are of 
the greatest benefit to the soil are, in the main, aerobes, and 
those that are injurious in their action are chiefly anaerobes. 
Bacteria, however, have more or less ability to adapt them- 
selves to a larger or smaller air supply. The fact that struc- 
ture, texture and drainage are so largely instrumental in 
regulating the quantity of air in the soil makes them im- 
portant factors in determining the kinds of bacterial processes 
that take place in a soil. 

159. Moisture. — Like other forms of plant life, bacteria 
require moisture for their growth. A soil may become so 
dry that the number of bacteria is decreased, but owing to 
their rapid multiplication the number soon increases with 
a replenished moisture supply. An excess of water may 
decrease the number or change the character of the flora 



Fig. 23. — Diagram showing the relative 
sizes of bacteria and some soil particles. 
(A) a fine sand particle, (B) a large clay 
particle, (C) a few soil bacteria. All are 
magnified at the same rate. 



THE GERM LIFE OF THE SOIL 129 

by cutting off the air supply. A well-drained soil in good 
tilth affords the best moisture conditions for the develop- 
ment of desirable bacteria. 

160. Temperature. — It is seldom that soil temperatures 
become sufficiently high to interfere with bacterial activity, 
and then it is only near the surface. Freezing does not 
kill most soil bacteria, but it renders them inactive during 
the frozen period. It is in the early spring that temperature 
is an important factor so far as its effect on bacteria is con- 
cerned. At that season it is desirable to warm the soil 
as rapidly as possible. 

161. Organic matter. — Many forms of bacteria utilize 
the organic matter of the soil as a source of food supply. 
Others thrive without any organic matter. For the proper 
functioning of a normal bacterial flora there should be a 
good supply of organic matter in the soil. 

162. Soil acidity. — ■ Most of the useful bacteria make 
their best growth in a soil that shows no acidity. This is 
notably true of those bacteria that assist in the process 
of making organic nitrogenous matter suitable for use by 
plants, and also the symbiotic bacteria of alfalfa and red 
clover. One of the important effects of lime is the increased 
activity of beneficial soil bacteria. 

163. Bacteria in relation to soil fertility. — We have now 
discussed the conditions under which, soil bacteria grow. 
The next step will be to describe the various processes by 
which they increase soil fertility and also, to some extent, 
by which they unfavorably influence soil productiveness. To 
do this they will be discussed in the order stated in § 155. 
The reader must, however, bear in mind that there are doubt- 
less many bacteriological processes in the soil regarding 
which nothing is known. 

164. Action on mineral matter. — There are, without 
doubt, microorganisms that act on mineral matter in soil, 

K 



130 SOILS AND FERTILIZERS 

attacking the insoluble substances and rendering them more 
soluble. The phase of this subject that is of most apparent 
agricultural importance is the effect of microorganisms 
on the very difficultly soluble rock or bone phosphoric acid, 
converting it into phosphoric acid available to plants. 
In laboratory experiments with pure cultures of bacteria 
these changes have been found to occur. There has also 
been found to take place a reverse process by which the more 
easily soluble phosphoric acid is converted into the less 
soluble one. . There is, at present, no way by which man can 
control this operation in the soil. It has been held that the 
presence of a large quantit}^ of organic matter will make the 
phosphoric acid of rock readily available. The results of 
experiments with raw rock phosphate and farm manure do 
not always confirm this idea. Under some conditions the 
dominant process may be the conversion of difficultly soluble 
into readily soluble phosphoric acid, while under other 
conditions the reverse may take place. 

165. Decomposition of non-nitrogenous organic matter. 
— There is much organic matter on the surface or in the 
plowed soil that contains no nitrogen. The cell walls of 
plants, and the sugars, starch and fats of plants contain no 
nitrogen. These substances are broken down by bacteria, 
passing through different stages among which acids occur, 
and finally being resolved into carbon dioxide and water. 
We have seen that the plant uses carbon dioxide as food 
material, and we may now understand the cycle through 
which the carbon of this gas goes. Plants absorb carbon 
dioxide through their leaves, decompose it and use the carbon 
in their tissues. After the plant is dead, the tissues decom- 
pose and carbon dioxide is again formed and passes into the 
air. Just as higher plants live and grow by using carbon 
from carbon dioxide, so bacteria live and grow by using the 
carbon of plant tissues. 



THE GERM LIFE OF THE SOIL 131 

166. Decomposition of nitrogenous organic matter. — 
The main difference between the decomposition of non- 
nitrogenous and nitrogenous organic matter is that in the 
latter nitrogen and usually sulfur play a part. The sulfur 
is not of so much importance, but it is very necessary that 
we should follow the various processes through which nitro- 
gen is transformed from organic substances into the final 
forms in which it is again used by plants or returned to the 
air. These processes will be treated under the following 




A B C D 

Fig. 24. — Appearance of some soil germs under the microscope. (A) free 
living nitrogen-fixing bacteria (Azotobacter), (B) bacteria that cause one 
step in the production of nitrates from ammonia (Nitrosomonas), (C) nitro- 
gen-fixing bacteria from the nodules of leguminous plants (Radicicola), 
(D) ammonia-forming bacteria (Proteus vulgaris). 

heads : (1) ammonification ; (2) nitrification ; (3) denitri- 
fication. 

Organic nitrogenous matter when it first enters the soil 
as plant or animal remains or as solid farm manure or green- 
manure is largely in the form of what are known as proteids. 
As soon as such material is incorporated in any normal 
soil, decomposition begins and the rate at which it proceeds 
depends on the character of the soil in which the process 
is going on. There are several different forms of bac- 
teria that are capable of decomposing proteins and there 
are always enough of these in any arable soil to do the work 
if the soil has the proper moisture, ventilation and heat and 
is not acid. 



132 SOILS AND FERTILIZERS 

167. Ammonification. — Various intermediate products 
occur in the breaking down of proteids, but we are concerned 
chiefly with the product known as ammonia. This is the 
nitrogenous substance contained in many fertilizers, and 
it may be used by some crops directly as food material. 
Rice, for instance, and probably other swamp plants can 
use ammonia better than any other form of nitrogen. Even 
some upland crops like corn, peas, barley and potatoes can 
use it, but not as well as they can the form of nitrogen into 
which ammonia is transformed by the next fermentation, 
namely nitrification. 

It may be well to say, in passing, that there are some other 
products intermediate between proteids and ammonia that 
are directly used by plants, and it is altogether likely that 
farm manure owes part of its great fertilizing value to some 
of these substances that it may possess. 

168. Nitrification. — This is the final step in the prepara- 
tion of nitrogen for use by most agricultural plants, for it is 
in the form produced by nitrification that nitrogen is most 
useful to most crops. This form is called nitrates. Like 
ammonification this fermentation goes on in any normal 
soil if the ammonia is there for it to work on, and also like 
ammonification the conditions of temperature, air supply, 
moisture and lime must be satisfactory or the process will 
be so slow that plants will suffer for nitrogen. 

There has been some question as to whether heavy manur- 
ing with organic manures results in a decreased nitrification. 
While this may be the case where farm manure is used in 
very heavy dressings of as high as fifty to a hundred tons 
to the acre, as is sometimes done in truck crop gardening, 
it is not likely to be the case in soils in which ordinary field 
crops are grown. 

169. Effect of soil aeration on nitrate formation. — One of 
the most important conditions that must obtain, if ammon- 



THE GERM LIFE OF THE SOIL 



133 



ification and nitrification are to proceed rapidly, is an ade- 
quate supply of air in the soil and this can only be secured 
by thorough tillage. This is illustrated by an experiment 
in which columns of soil eight inches in diameter and eight 
inches high were removed from a field of clay loam and car- 
ried to the greenhouse without disturbing the structure of 
the soil as it existed in the field. At the same time vessels 
of similar size were filled with soil dug from a spot near by. 
These represented unaerated and aerated soils respectively, 
because one had been undisturbed, while the other had 
been thoroughly exposed to the air. Both were kept at the 
same temperature and moisture content in the greenhouse 
but no plants were grown in them. The production of 
nitrates was as follows : 

Table 30. — Formation of Nitrates in Unaerated and in 
Aerated Soil 



Times of Making Analyses 


Nitrates in Dry Soil, Parts per 
Million 




Unaerated soil 


Aerated soil 


When taken from field .... 
After standing one month . . . 
After standing two months . . 


3.2 
4.2 
9.0 


3.2 
17.6 
45.6 



170. Effect of temperature on nitrate formation. — There 
is a considerable range of temperature through which the 
process of nitrate formation proceeds with more or less 
intensity. Freezing stops the fermentation, but does not 
kill the bacteria, whose activity is resumed when the tempera- 
ture rises to about 40° F. and increases until a temperature 
approaching 75° to 85° F. is reached, after which the in- 
tensity gradually diminishes. At 110° F. and above, there 
is little formation of nitrates. 



134 



SOILS AND FERTILIZERS 



The more rapidly a soil becomes warm in the spring, the 
sooner will nitrates be formed. Crops like winter wheat 
will often begin growth before the soil is sufficiently warm 
to admit of the rapid formation of nitrates and, as winter 
rains will have leached from the soil nitrates that accumu- 
lated during the preceding year, the plants often suffer 
seriously from lack of nitrogen. 

It is not often that the soil for several inches below 
the surface becomes hot enough, even in midsummer, to 
interfere with nitrate formation. Crops that make their 
growth in late spring or summer are not likely to suffer 
for nitrates unless the total supply of nitrogen is deficient. 

171. Effect of sod on nitrate formation. — In soil on 
which there is a good stand of grass very little nitrate is 
ever found. Sod apparently has a depressing influence on 
nitrate formation. On the same type of soil as that used in 
the experiment last described, the average quantities of 
nitrates for each month of the growing season in the surface 
eight inches of sod land, as compared with corn land under 
the same manuring, were as follows : 

Table 31. — Nitrates in Soil Under Sod and Under Corn 



Month 



April 
May 
June 
July 
August 



Nitrates in 


Dry Soil, Parts per 




Million 


Sod Land 


Corn Land 


8.9 







3.0 




17.1 


2.4 




40.3 


4.0 




194.0 


5.4 




186.7 



There was more nitrogen contained in the corn crop than 
there was in the timothy crop, so that the larger quantity 



THE GERM LIFE OF THE SOIL 135 

of nitrates in the corn land cannot be attributed to failure 
of the plants to remove it. Grass appears to have a decidedly 
depressing effect on the process of nitrate formation, and 
this may be one reason why grass is generally a detriment 
to the growth of young orchards. 

172. Depths at which nitrate formation takes place. — 
It is probable that the processes by which nitrates are formed 
are, in humid regions, confined largely to the furrow slice 
of soil. Nitrates found below that point have probably 
been, in large measure, washed down from above. The sub- 
soil in such a region is not a very favorable medium for these 
processes. In arid and semi-arid regions, however, the case 
is different. Here the distinction between surface soil and 
subsoil is not so marked, and owing to the rich and porous 
nature of these subsoils nitrification may proceed at con- 
siderable depths. 

173. Loss of nitrates in drainage. — It has already been 
shown that there is a large removal of nitrates in drainage 
water (§ 121). As nitrogen is the most expensive of fer- 
tilizer constituents every effort should be made to prevent 
this loss. A very effective way to do so is to have a crop 
growing on the land during all of the growing season. A 
comparison of the loss from the planted and unplanted soil, 
in the paragraph referred to, will show how effective a crop 
is as a means of preventing loss of nitrates in drainage 
water. 

Hall states that nitrates formed during the summer or 
the autumn of one year are practically all removed from the 
soil of the Rothamsted fields before the crops of the following 
year have advanced sufficiently to use them. 

174. Denitrification. — After nitrates have been formed 
by the processes that have just been described, there are 
other bacteria or some of the same bacteria acting under 
different conditions that attack the nitrates and convert 



136 SOILS AND FERTILIZERS 

them into other substances. There are three different pro- 
cesses and three distinct products that may result. These 
are : (1) reduction of nitrates to ammonia ; (2) reduction 
of nitrates to free nitrogen ; (3) conversion of nitrates into 
organic nitrogenous substances. All of these fermentations 
result in a conversion of the more easily available forms of 
nitrogen into less available, and in the case of the production 
of free nitrogen there is a loss of nitrogen from the soil, as 
the free nitrogen is a gas and passes off into the air. 

Most of the bacteria that effect these changes do so only 
when there is a limited supply of air, so that a thorough aera- 
tion of the soil practically prevents denitrification. Straw 
apparently induces denitrification when conditions are at 
all favorable for that process. 

The addition of a nitrate fertilizer to a well-drained soil 
receiving farm manure is not likely to result in a loss of 
nitrates unless the dressing of manure has been extremely 
heavy. At the Rothamsted Experiment' Station, where 
large quantities of nitrate of soda are used every year in 
connections with annual dressings of farm manure, the nitrate 
produces nearly as large an increase when applied to the 
manured as when added to the unmanured plat. 

Very heavy applications of farm manure, of fifty tons to 
the acre or more, may temporarily interfere with formation 
of nitrates. The plowing under of large quantities of straw 
and even, under some conditions, green-manures may have 
this effect. 

175. Nitrogen fixation. — Another and very important 
bacteriological process is the transfer of nitrogen from the 
atmosphere to the soil. This process is termed " nitrogen 
fixation " and it may occur either with the assistance of higher 
plants, or without. The first of these is called nitrogen 
fixation through symbiosis with higher plants, the second 
nitrogen fixation by soil organisms not associated with plants. 



THE GERM LIFE OF THE SOIL 137 

The importance of this process to soil productiveness may 
be realized when it is considered that nitrogen is the most 
expensive of all the ingredients of commercial fertilizers, 
and that many pounds to the acre msiy be secured by en- 
couraging the growth of the bacteria concerned in the op- 
eration. 

176. Nitrogen fixation through symbiosis with higher 
plants. — The value of certain plants as soil improvers has 
long been recognized, and within the last half century their 
ability to improve soil has been traced to their property of 
taking nitrogen from the air and leaving it in the soil. The 
plants that do this belong, with a few exceptions, to the 
family of legumes. 

The method by which nitrogen is transferred from the air 
to the soil is not perfectly understood, but it appears to 
be somewhat as follows : 

On the roots of leguminous plants are found nodules or 
tubercles, which are large enough to be seen with the naked 
eye, and in which live the bacteria that remove the nitrogen 
from the soil air and convert it into nitrogenous organic 
matter, that then becomes a part of the host plant. As a 
consequence legumes are very rich in nitrogen, and the 
tubercles contain an especially large quantity. When the 
roots and nodules decay and when the aboveground part of 
the plant is plowed under, the nitrogenous matter they con- 
tain becomes a part of the soil. 

If the nitrogen-fixing bacteria are not present in the soil 
or other medium in which the legumes grow, no nodules 
will be formed and no atmospheric nitrogen will be fixed. 
The plant must then live on the combined nitrogen of the 
soil just as other plants do and consequently it does not 
serve to increase the store of soil nitrogen. In fact, the 
reverse occurs, for on account of the high nitrogen content 
of legumes, they withdraw, under these conditions, large 



138 SOILS AND FERTILIZERS 

quantities of nitrogen from the soil. Even when the nitro- 
gen-fixing bacteria are present, leguminous plants may draw 
much of their nitrogen from the nitrates in a soil that is 
rich in these substances. As a result, less nitrogen is taken 
from the air and if the crop is removed the quantity of nitro- 
gen remaining in the soil may be no greater than before the 
legume was planted. 

177. Soil inoculation for legumes. — After it had been 
discovered that leguminous plants acted as hosts for bacteria 
that draw nitrogen from the soil air, the idea at once pre- 
sented itself that soils not containing these bacteria could be 
inoculated with them, and thus be made much more suitable 
to the growth of legumes. It has been found to be practi- 
cable to accomplish this inoculation by spreading on the land 
soil from a field on which the kind of legume it is proposed 
to plant has grown successfully. The fact that inoculation 
by means of soil from other fields may possibly transmit 
weed seeds and fungous diseases, and that it also necessitates 
the transportation of a great bulk and weight of material has 
led to numerous efforts to inoculate soil by means of pure 
cultures of bacteria. This has been fairly successful in re- 
cent years, but the surest way is by the use of soil. However, 
pure cultures may be obtained from most of the agricultural 
experiment stations and from the U. S. Department of Agri- 
culture, Washington, D. C. 

It must be borne in mind that when soil is used for inocula- 
tion it must come from a field that has produced a good crop 
of the same land of legume that is to be planted on the inoc- 
ulated field, also that the soil must not be allowed to become 
very dry, as that is likely to kill the bacteria. The inoculat- 
ing soil is applied after plowing and is harrowed in. 

If inoculation is to be successful, the soil on which the 
legume is to be planted must be of a nature favorable to the 
legume, otherwise growth will not be normal in spite of 



THE GERM LIFE OF THE SOIL 



139 



inoculation. The conditions favorable for legumes are the 
same as for most upland crops, namely good drainage and 
good tilth, while for red clover, peas or alfalfa the soil should 
have an abundant supply of lime. 

Not only is the yield of an alfalfa crop greatly increased 
by the presence of the nitrogen-fixing organisms and also 



$0 animal 




~ iriTERMEDlATE PRODUCTS 
Carbon dioxide, etc 

*'- - • -. _' ' yi/VMONineATion 

"" — /inflow/* 



Titrates 
WTRinCATIOH* 



Fig. 25. — The cycle through which nitrogen passes in its movements 
among soil, plant, animal and atmosphere. Solid lines in the diagram indi- 
cate the usual transformations of nitrogen. Dotted lines indicate the occa- 
sional transformations. 



of lime, but the percentage of nitrogen that the crop contains 
is thereby increased. 

178. Nitrogen fixation by free living germs. — In addi- 
tion to the nitrogen-fixing bacteria described above, there 
exist in many soils germs that are able to take nitrogen from 
the atmosphere and convert it into nitrogenous organic mat- 
ter without the aid of a host plant. How extensively these 
organisms operate is difficult to say. In poor land they are 
often effective in recouping the supply of soil nitrogen, but 
it is doubtful to what extent they function in rich soil. At 
the Rothamsted Experiment Station one of the fields had 
been allowed to lie unused for many years because it was too 



140 SOILS AND FERTILIZERS 

poor to cultivate. It grew up mainly to grass, with a very 
few legumes, and in the course of twenty years it had gained 
nitrogen at the rate of twenty-five pounds to the acre an- 
nually. With the exception of about five pounds to the acre 
that was brought down by rain, dust and the like, the accu- 
mulation was doubtless due to the free-living germs. 

QUESTIONS 

1. Explain the difference between the directly injurious and the 
indirectly injurious effect of soil germs on plant growth. 

2. Are the numbers of bacteria in soils rather uniform, or do 
they vary greatly in different soils ? 

3. Describe the relation of soil bacteria to the air supply. 

4. Their relation to moisture. 

5. Their relation to temperature. 

6. Their relation to organic matter. 

7. Their relation to soil acidity. 

8. Their relation to soil fertility. 

9. Describe the cycle- through which carbon passes from plant 
to soil and back to air again. 

10. Explain the fermentation known as ammonification. 

11. Describe what is meant by nitrification. 

12. How do soils of arid and humid regions differ in respect to 
the depths at which nitrate formation occurs ? 

13. Why does nitrate formation not take place in early spring ? 

14. Describe three fermentations by which the nitrogen of ni- 
trates is converted into other forms. 

15. Describe the two processes by which atmospheric nitrogen 
is fixed in the soil by germs. 

16. Describe the cycle through which nitrogen passes from the 
plant to soil and back to plant again. 

LABORATORY EXERCISES 

Exercise I. — Test for nitrates in soil. 

Materials. — A rich garden loam, a 500 c.c. vessel for mixing 
the soil and water, wooden stirrer, funnel and filter paper, hydrate 
of lime, water bath, ammonium hydrate solution, evaporating dish, 
phenoldisulphonic acid. 



THE GERM LIFE OF THE SOIL 141 

The phenoldisulphonic acid is prepared as follows : To 37 grams 
of concentrated sulphuric acid add 3 grams of pure crystalline phenol. 
Heat for six hours in a lightly stoppered flask set in boiling water. 

Procedure. — To 50 grams of soil in the 500 c.c. container add 
250 c.c. of distilled water. Add 1 gram of hydrate of lime to floccu- 
late the soiL Stir three minutes and allow to stand 20 minutes. 
Pipette off 25 or 30 c.c'. of the clear supernatant liquid and filter it. 
Evaporate 10 c.c. of the filtrate to dryness over a water bath in an 
evaporating dish. Moisten with a few drops of phenoldisulphonic 
acid and stir well. Allow to stand a few minutes. Dilute with a 
few cubic centimeters of water and neutralize with ammonia. The 
development of a yellow color is an indication of the presence of 
nitrates and its intensity is a measure of the amount. 

Exercise II. — Test for ammonia in soil. 

Materials. — A small portion of the soil solution obtained in 
Exercise I, and Nessler's solution. 

The Nessler's solution is made as follows : To a 250 c.c. 
solution of potassium iodide (made by dissolving 63 grams in 250 
c.c. of ammonia-free water) add a saturated solution of mercuric 
chloride until the precipitate nearly all redissolves. "Now add 250 
c.c. of a solution of potassium hydrate (150 grams to 250 c.c. of 
water) . Make up the whole solution to one liter. Allow to stand 
until any precipitate has settled before using. Keep in well-stop- 
pered bottle in the dark. 

Procedure. — To ten cubic centimeters of the soil extract add a 
few cubic centimeters of Nessler's solution. The development of a 
light yellow is an indication of ammonia. 

Exercise III. — Factors affecting nitrification. 

Materials. — Same as Exercise I plus four 100 c.c. graduated cyl- 
inders. Use moist acid soil from beneath sod. 

Procedure. — Place four 50-gram portions of a moist soil from 
beneath sod in 8-ounce wide-mouth bottles. Bring soil of bottle 
No. 1 to optimum moisture*. Saturate soil of bottle No. 2 to give 
poor aeration. Thoroughly mix one gram of carbonate of lime to 
bottle No. 3 and one gram of lime plus one-tenth gram of ammonium 
sulfate with soil of bottle No. 4. Raise both to optimum moisture. 
Stopper all bottles lightly with cotton and allow to stand in a warm 
room for a week or ten days. 

Develop nitrates from these samples as directed in Exercise I. 
Pour developed solutions into 100 c.c. graduates and dilute to a con- 



142 SOILS AND FERTILIZERS 

venient mark. Compare the intensity of color from the various 
treatments and explain the results obtained. How may the results 
be applied to field practice ? 

Exercise IV. — Examination of legume nodules. 

Visit fields of red clover, vetch, alfalfa, peas, etc., and with a spade 
carefully uproot some of the plants and search for nodules. Note 
the number, size and location of the nodules on the various legumes. 
If suitable specimens of roots bearing nodules are found it might be 
feasible to preserve them for exhibition purposes. They may be 
satisfactorily preserved in glass cylinders filled with water to which 
a few drops of formalin have been added. The cylinders should be 
tightly stoppered to prevent evaporation. 

Exercise V. — Examination of nodule bacteria. 

If the instructor has an oil immersion microscope available, with 
staining mixtures and other facilities for preparing slides of bacteria, 
this would be a desirable demonstration. The pupil would then 
gain a first hand knowledge of bacteria. Other soil organisms might 
also be mounted for class use. 

Exercise VI. — Soil inoculation. 

If the instructor could arrange in some way to cooperate with a 
near-by farmer in inoculating his soil by some of the means available 
for the purpose, this would be a valuable demonstration for the pupils 
to attend. Actually seeing a thing done is worth much more than 
mere class room study. 



CHAPTER X 

SOIL AIR AND SOIL TEMPERATURE 

The volume of soil air depends on the volume of pore space 
that is not filled with water. It is, therefore, evident that 
ordinarily the non-capillary or larger spaces are the ones 
that contain air. It will be remembered that the most im- 
portant conditions that favor a large pore space in soils are : 
(1) granular structure, (2) presence of organic matter. In 
any soil the pore space may change from time to time with 
the structure and the application of organic matter. 

179. Soil air contained largely in non-capillary spaces. — 
The removal of water allows more space to be filled with 
air. Immediately after a heavy rain much of the pore space 
of the surface soil is filled with water. After this has had 
time to drain away only the capillary spaces remain filled, 
but capillary water is lost much more slowly. It is the non- 
capillary pore space that, during the greater part of the time, 
constitutes the air space of the soil. As a compact condition 
of soil results in smaller pore spaces and consequently in 
more capillary spaces, it causes a decrease in the volume of 
air. 

180. There may be too much or too little soil air. — Soil 
air is a necessary constituent of a productive soil, as will be 
explained later, but it is not always the case that the more 
air space in a soil the better it is for crop production. Very 
large air spaces, like those found in a cloddy soil, allow the soil 
to dry out too readily. Up to a certain limit a good supply 

143 



144 SOILS AND FERTILIZERS 

of soil air is desirable, but there can be too much. On the 
other hand, there may be too little. It may be assumed 
that when a soil is in a compact condition it has an insuffi- 
cient supply of air. 

181. Movement of soil air. — The rate at which air moves 
through a soil depends largely on the size of the pore spaces, 
rather than on their aggregate volume. Movement of air 
is necessary to ventilate the soil, just as it is to freshen the 
air in a house in which many persons live, or a public hall 
in which people congregate. Among the factors concerned 
with the movement of soil air are (1) movement of water, 
(2) diffusion of gases, (3) some minor conditions, like dif- 
ferences in temperature between atmospheric air and soil 
air, periodic changes in atmospheric pressure and suction 
produced by wind. 

182. Movement of water. — The movement of soil air 
caused by water is probably the most important of any. 
When rain falls, the surface soil first receives the water, 
which usually fills all of the spaces between the particles. 
As the water descends, air is driven from the pore spaces 
to make room for the water, the air escaping upward as the 
water goes downward, or else being forced out through the 
drainage channels below. The movement of air proceeds 
to the depth of the water table. Fully one-fourth of the 
air in a soil may be forced out by a normal change in the 
moisture content of a soil. As the soil dries out air returns. 

183. Diffusion of gases. — Owing to the difference in com- 
position between the atmospheric air and soil air, there is a 
tendency for them to mix, and this process would go on until 
the two had the same composition, were it not for the fact 
that gases are continually being formed in the soil and thus 
prevent the soil from attaining the same composition as the 
atmospheric air. The process of diffusion is, therefore, con- 
tinuous. 



SOIL AIR AND SOIL TEMPERATURE 



145 



The rate of diffusion depends on the total volume of the 
pore spaces and not on their average size. A soil in good 
tilth is therefore in suitable condition for permitting dif- 
fusion of atmospheric and soil air. 

184. Composition of soil air. — The greater part of the 
soil air, like atmospheric air, is composed of nitrogen and 
oxygen. The principal difference between soil air and 
atmospheric air, in respect to composition, is that the former 
contains more moisture and more carbon dioxide. The 
moisture comes from evaporation of water in the soil. 
The carbon dioxide is produced for the most part by the 
germs in the soil and by roots. The following table shows 
how soils may vary in their content of carbon dioxide. 



Table 32. 



Percentage of Carbon Dioxide in Air of Differ- 
ent Soils at Same Depth 



Character of Soil 



Forest soil 

Clay soil 

Asparagus bed not manured for one 

year 

Asparagus bed freshly manured . 
Sandy soil six days after manuring . 
Vegetable mold compost 



Percentage Composition 



Carbon 
Dioxide 



0.87 
0.66 



0.74 
1.54 
2.21 
3.64 



Oxygen 



19.61 
19.99 

19.02 

18.80 

16.45 



Nitrogen 



79.52 
79.35 

80.24 
79.66 

79.91 



Soils that are high in organic matter and in which decom- 
position goes on readily, usually have a large quantity of 
carbon dioxide. 

185. Production of carbon dioxide in soils. — It has 
already been shown that plant roots give off a considerable 
quantity of carbon dioxide throughout the growth of the 



146 SOILS AND FERTILIZERS 

plant (§ 126). This, however, does not account for the 
gas that is formed in soils on which no plants grow. For 
this the germ life of the soil is responsible. These organisms 
consume fresh air and give off carbon dioxide in the process 
of their growth. In soils that contain a large and active pop- 
ulation of microorganisms there is more carbon dioxide formed 
than in a more nearly sterile soil. 

It has been estimated that in an acre of ordinary soil to a 
depth of four feet the germs produce between sixty-five and 
seventy pounds of carbon dioxide a day for two hundred 
days in the year, and that, during the growing period, the 
roots of oats or wheat would give off nearly as much in an 
acre. 

186. Conditions that affect the quantity of carbon dioxide 
in soils. — As carbon dioxide is heavier than air, the quantity 
increases with depth. In warm weather more carbon dioxide 
is formed than in cold because the germs are more active. 
The soil moisture exerts an influence by furnishing the 
necessary moisture for the germs. A very dry or a very 
wet soil is not favorable to the production of the gas. More 
carbon dioxide is given off by roots during the blossoming 
period than at other stages of plant growth, consequently 
the carbon dioxide content of soil air is highest about the 
time the plants are in blossom. 

187. Usefulness of air in soils. — The three gases, oxygen, 
nitrogen and carbon dioxide, that go to make up practically 
all of the soil air are useful in bringing about those processes 
that make soils fertile. Each one of these gases has its 
function in contributing to plant growth either directly, or 
by taking part in processes that render the soil more habitable 
to plants. The functions of each gas will be discussed sep- 
arately. 

188. Oxygen. — This constituent of soil air serves the 
following uses : (1) As a direct food material for plants, 



SOIL AIR AND SOIL TEMPERATURE 147 

and as a means of promoting in the plant the processes 
necessary to its growth. Roots of most crops must have 
access to a supply of oxygen. 

(2) Decomposition of plant residues and other organic 
matter in soils requires the presence of ox3^gen, and without 
decomposition these materials would accumulate in the soil 
to the exclusion of higher plant life. Decomposition is 
also of use in the production of carbon dioxide, the function 
of which will be discussed later, and in the formation of 
compounds of organic matter with mineral matter, decom- 
position serves to increase the availability of mineral sub- 
stances (see § 118). 

(3) The process by which the nitrogen of organic matter is 
converted into nitrates can proceed only in the presence of 
oxygen. 

189. Nitrogen. — Although not so essential as oxygen, 
there is at least one important service that is rendered by 
the nitrogen of soil air. This is to furnish the nitrogen-fixing 
organisms with a supply on which they may draw to produce 
the nitrogenous compounds that become incorporated in 
leguminous plants, or that are formed directly in the soil by 
the free-living nitrogen fixers. 

190. Carbon dioxide. — The principal service that carbon 
dioxide renders is in acting as a solvent for the mineral matter 
of the soil. For this purpose it is itself first dissolved in 
soil water, in which condition it is a weak acid, but although 
weak, its universal presence and constant action make 
it an effective solvent. It dissolves from the soil more or 
less of all the nutrient substances required by plants in dis- 
tinctly greater quantities than does pure water. 

A number of experiments in which carbon dioxide was 
artificially brought in contact with soil on which plants were 
growing have resulted in producing larger crop yields than 
were obtained from soil not so treated. It cannot be con- 



148 SOILS AND FERTILIZERS 

eluded from this that an artificial supply of carbon dioxide 
will always be beneficial, but it does indicate that carbon 
dioxide assists in making the plant nutrients more available, 
although in many soils the natural supply is sufficient for its 
maximum effect. 

191. Control of the volume and movement of soil air. — 
It will be gathered from the preceding paragraphs that a 
good supply of air in soil with opportunity for its exchange 
with atmospheric air is desirable for a number of reasons. 
These conditions can be controlled by man to some extent. 
In fact those operations that usually promote tilth serve at 
the same time to effect a desirable condition of the soil with 
respect to air. The operations by which man may control 
soil air are as follows : 

1. Tillage of all kinds, when properly done and at the 
right time, increases the volume of air in most soils by help- 
ing to form the crumbly structure, and by disposing of 
excess water. 

2. Both farm manure and lime cause an increase in the 
carbon dioxide content of soil air, the former by contribut- 
ing organic matter that finally decomposes, the latter by 
hastening decomposition processes. 

3. Underdrainage by removing water from the pore 
spaces increases the volume of air and causes its movement. 

4. Cropping produces channels through the soil where 
roots have decayed, and these openings, on account of their 
large number and ramifications through the soil, aid greatly 
in increasing the volume of soil air. 

192. Soil temperature. — The temperature of the soil 
may influence plant growth both directly and indirectly. 
The direct effect is to be found in the plant itself, the roots 
of which require a certain degree of heat before they begin 
to function. A temperature somewhat above the freezing 
point is necessary for this purpose, some common plants 



SOIL AIR AND SOIL TEMPERATURE 149 

beginning growth slightly above. that point, while others 
need several degrees higher temperature. This is also true 
of the germination of seeds. The optimum temperatures 
for both plants and seeds are considerably higher. A tem- 
perature may be reached at which both plant growth and 
seed germination may be inhibited, but soils rarely reach 
such a degree of heat, except at the immediate surface. 
The problem with soils usually consists in bringing them to 
a sufficiently high temperature in the spring. 

The indirect influence of temperature is exerted through 
the germs that affect plant growth. These, like higher 
plants, require a certain degree of warmth before growth 
begins and a still higher temperature before they reach their 
full activity. It often occurs that crop growth is well under 
way before the soil is sufficiently warm for germs to function 
actively, and consequently growth is checked by the need 
of nitrates, which have not been formed in sufficient quantity 
on account of the low temperature. This condition is often 
demonstrated by the yellow color of the leaves. 

193. Sources of soil heat. — The greater part of the heat 
that enters the soil comes directly from the sun. The other 
possible sources are the organic matter in the soil and heat 
from the interior of the earth. Heat produced by the de- 
composition of organic matter may sometimes be a factor 
when the proportion is large, as is the case in hotbeds and 
some gardens, but ordinarily it may be left out of considera- 
tion, as may also the heat transmitted from the center of 
the earth. 

194. Relation of soil temperature to atmospheric tem- 
perature. — Changes in temperature of the atmosphere are 
transmitted to the soil, although the extremes are never so 
great in the soil as in the atmosphere, except at the im- 
mediate surface, and the extremes become less as the depth 
increases. In summer the temperature of the surface soil is 



150 



SOILS AND FERTILIZERS 



sometimes higher than the average temperature of the at- 
mosphere, or even than the maximum air temperature. The 
soil below is cooler and continues to decrease in temperature 
as the depth increases. For that reason a cellar is usually 
cooler in summer than is the outside air. On the other hand, 
the soil does not become as cold as does the atmosphere in 
winter, and below a few feet, in temperate regions, the soil 
does not freeze. The following table gives the mean atmos- 
pheric temperatures, and the soil temperatures, at different 
depths by months throughout an entire year. 



Table 33. 



Average Monthly Temperature Readings Taken 
at Lincoln, Nebraska 



January . 

February 

March 

April . . 

May . . 

June . . 

July . . 

August 

September 

October . 

November 

December 

Average 

Range 



Aveeage op Twelve Years 



Air 



25.2 
24.2 
35.8 
52.1 
61.9 
71.0 
76.0 
74.5 
67.6 
55.5 
38.7 
28.3 
50.9 
51.8 



3 Inches 
Deep 



27.8 
27.3 
37.2 
56.0 
67.5 
78.0 
83.6 
81.3 
73.4 
58.4 
40.9 
31.4 
55.3 
56.3 



12 Inches 
Deep 



31.2 
30.2 
35.4 
49.3 
60.7 
69.9 
75.7 
75.7 
69.2 
57.8 
44.7 
35.2 
52.9 
45.5 



36 Inches 
Deep 



38.5 
35.5 
35.8 
43.8 
53.3 
61.3 
67.4 
69.8 
67.6 
61.3 
52.2 
43.3 
52.5 
34.3 



195. Factors that modify soil temperature. — There are 
a number of conditions that exert an influence on the tem- 
perature of the soil, important among which are (1) the 
moisture content, (2) the color of the soil, (3) the slope of 
the land. 



SOIL AIR AND SOIL TEMPERATURE 151 

A wet soil is always a cold soil, because it requires about 
five times as much heat to raise the temperature of a pound 
of water through one degree of temperature as it does to 
heat a pound of dry soil to the same extent, and also because 
when the water becomes warm it evaporates and in so doing 
removes much heat from the soil. The evaporation of a 
pound of water from a cubic foot of soil will reduce the tem- 
perature of the soil about ten degrees Fahrenheit. Provision 
for having the water drain away from the land in the spring- 
rather than evaporate will make a great difference in the 
warmth of the soil. A dark soil absorbs more heat than a 
light colored one. This is enough to make some practical 
difference in a region having a short growing season. 

Land that slopes to the south absorbs more heat, in the 
North Temperate zone, than does land having any other 
slope, and the nearer the slope comes to making a right 
angle with the sun's rays the more heat it will absorb. 
An east or west slope receives more heat than does a north 
slope. For this reason a north slope is especially favorable 
for grass land, because grass is more injured by midsummer 
heat than by lack of sunshine. 

196. Control of soil temperature. — As water is the 
substance in the soil most difficult to heat, it is evident that 
good drainage, that will remove the excess water derived 
from melted snow and ice, is the most effective means of 
warming land in the spring, in order that it shall be fitted 
for planting. If water can pass out of the soil by under- 
drainage it then becomes desirable to curtail evaporation, 
and this may be done by surface tillage. Evaporation of 
water removes, as we have seen, large quantities of heat. 
If water can be removed in any other way much heat is 
saved. In regions having hot spring days the loss by evapo- 
ration may be so large that more water is removed than is 
desirable and yet the soil may lack the necessary warmth, 



152 SOILS AND FERTILIZERS 

Sandy soils are less likely to be cold in spring than are 
clay soils, because the former usually hold water less tena- 
ciously. In , vineyards a covering of stones on the soil 
has been found to facilitate the warming of the soil in the 
spring, but it is doubtful whether, in view of their other dis- 
advantages, stones are desirable. 

Good tilth is, next to drainage, the be^t aid to warming soil 
in spring, as it allows the water to pass down into the lower 
soil and thus decreases evaporation from the surface. Har- 
rowing in the spring produces this result, while rolling, by 
compacting the surface, increases evaporation and cools the 

soil. 

QUESTIONS 

1. Describe the conditions that govern the volume of air in soils. 

2. State the two principal factors that affect the movement 
of soil air. 

3. How does the composition of soil air differ from that of 
atmospheric air ? 

4. What are the sources of carbon dioxide in soil air ? 

5. What are the functions of the oxygen of soil air ? 

6. What are the functions of the nitrogen of soil air ? 

7. What are the functions of the carbon dioxide of soil air? 

8. In what ways may the volume and movement of soil air 
be controlled ? 

9. Describe the direct and the indirect effect of temperature 
on plant growth. 

10. What are the sources of soil heat ? 

11. Describe three factors that modify soil temperature. 

12. By what means may soil temperature be controlled? 

LABORATORY EXERCISE 

Exercise I. — Movement of soil air as influenced by texture and 
moisture. 

Materials. — Dry sand, dry clay loam, 6" funnels, cotton, aspi- 
rating bottles (10 liter). 

Procedure. — Place a large funnel through the cork of an aspi- 
rating bottle, fill to the mark with water, as shown in Fig. 26. 
Place a small piece of cotton in the bottom of the funnel and fill with 



SOIL AIR AND SOIL TEMPERATURE 



153 



a definite volume of sand. Now start as- 
piration by opening the water-cock of the 
bottle. When aspiration has become con- 
stant, note time necessary to draw one liter 
of air through the sand. 

Using clay loam in place of sand, run 
the experiment again, bringing the water in 
the aspirating bottle up to its original mark 
before starting. The time necessary to pull 
a liter of air through each soil serves as a 
measure of the comparative rate of possible 
air movement through them. 

Without removing the clay loam from the 

funnel, add enough water to bring it to 

optimum moisture condition. Repeat the 

test above. Explain results. Fig. 26. — Apparatus 

-in tt mi, £ r. f° r studying the relative 

Rxercise II. - The presence of carbon rate of air movement 

dioxide in soil air. through soils. (A) soil in 

Materials. — Box of rich soil in good mois- funnel, (B) cotton sup- 

ture condition, flask, limewater, tubes.' ^J^m^ter*^ ^ 

Procedure. — Equip a flask or bottle as e ' wa er ' 

shown in Fig. 27 so that air from the soil may be sucked into the 

limewater. The turbidity of the limewater indicates the presence 

of carbon dioxide. 




i^ 



Suction 



Tube for iinlhdraujinq 
/ soil air 




Coarse sand 



Fig. 27. — Apparatus prepared for the demonstration of the presence of 
carbon dioxide in soil air. 



154 



SOILS AND FERTILIZERS 



First pull atmospheric air into the limewater for five minutes. 
Note results. Now connect flask to tube extending into the soil and 
draw in soil air. What conclusions do you come to regarding the 
relative carbon dioxide content of soil air and atmospheric air ? 
What is the function of carbon dioxide in the soil ? 

Exercise III. — Production of carbon dioxide by bacteria. 

Materials. — Flask, limewater and moist 
rich soil. 

Procedure. — Place a small amount of 
limewater in a flask and then suspend in 
the flask over the limewater a bag of rich, 
moist soil. Stopper tightly and allow to 
stand for a week. Note the turbidity of the 
limewater. Explain the results. 

Exercise IV. — Temperature and color. 

Materials. — Coal dust and calcium hy- 
drate. Thermometers. 

Procedure. — Divide a small plat of 
smooth, level soil into three portions. 
Leave one part untouched, cover one with a 
thin coating of coal dust and the other with 
a coating of calcium hydrate. On a warm, 
sunny afternoon take the temperatures of 
each at one, three and six inches deep. 
Tabulate and give a practical explanation 
of the data obtained. 



< — 

" ~_ ■ = z — jt^JZ— "" ^ 



Fig. 28. — Production 
of carbon dioxide by 
germs in soil. (A) tight 
stopper, (B) flask con- 
taining limewater, (C) 
small bag containing 
moist soil suspended from 
stopper, (D) limewater. 



Exercise V. — Slope and temperature. 

Materials. — Thermometers. 

Procedure. — On a warm, sunny day take temperature at one, 
three and six inch depths on a south slope, north slope and level 
land, being careful to select for the observations soils having the 
same texture and moisture contents. Tabulate data and explain 
the practical relationships between temperature and slope of land. 

Exercise VI. — Drainage and temperature. 

Materials. — Soil, two jars, thermometer. 

Procedure. — Prepare two large jars of moist soil. Stir one until 
two or three inches of the top soil is dry. Add water to the other 
until it is saturated. Set these jars of soil in the sunshine out of 
doors on a warm day. After two hours take the temperature* of 
the two soils at one inch and three inches in depth. Tabulate data. 



CHAPTER XI 
NITROGENOUS FERTILIZERS 

We have seen that nitrogen exists in soils in several differ- 
ent forms, as organic matter, ammonia and nitrates, and that 
it may be transformed from one to another of these, depend- 
ing on the conditions that obtain in the soil itself. Ferti- 
lizers used for their nitrogen may have this nitrogen present 
in any one or more of these forms, and when incorporated 
with the soil, transformation will proceed according to the 
same laws that govern the soil nitrogen. This is important 
because nitrogen is more readily used by crops in some 
forms than in others. 

197. Relative quantities of the different forms of nitrogen 
in soils. — One would naturally expect to find the greater 
part of the supply of soil nitrogen in the most stable forms, 
and this is, in fact, the case. The uncombined nitrogen of the 
air constitutes the largest supply because of its diffusibility 
with the atmospheric air. Next in quantity is the nitrogen 
of organic compounds, ranging from 0.05 to 0.3 percent or 
1000 pounds to 6000 pounds to the acre in the furrow slice 
of ordinary arable land and slightly, but appreciably, soluble 
in water. In upland cultivated soils the nitrogen of nitrate 
salts forms the next largest supply, but rarely exceeds 20 
percent of the total combined nitrogen of the soil. 

In inundated soils, the nitrogen of ammonia salts and 
nitrites forms a larger proportion of the soil nitrogen than 
does the nitrate nitrogen, but in well-aerated soils these com- 
pounds exist in very small quantities. 

155 



156 SOILS AND FERTILIZERS 

198. Forms in which nitrogen is absorbed by plants. — 

The utilization of atmospheric nitrogen by leguminous plants 
and by a few others that have nodule-bearing roots has been 
established beyond question : but the extent to which this 
form of nitrogen may be utilized by other plants, or the kinds 
of plants that have the ability to use it, are subjects on which 
opinions differ. It is sufficient to say that such plants as 
red clover, alfalfa, peas, beans, vetch, and so on, are able to 
use atmospheric nitrogen. It must be remembered, however, 
that they also use nitrogen that is in the soil itself and that 
they may remove large quantities of this material. 

199. Nitrates as plant-food material. — Most upland 
plants used in agriculture appear to absorb most of their 
nitrogen in the form of nitrates. This it will be remem- 
bered is the final form in which nitrogen appears when ni- 
trogenous substances undergo normal decomposition in soil. 
The nitrogen of the various nitrogen carrying fertilizers is 
finally converted into nitrate in the soil. 

200. Absorption of ammonia by agricultural plants. — 
Ammonia is rarely found in soils, except when they are 
saturated with water. Plants like rice, that grow on water- 
covered soil, can utilize ammonia ; in fact, rice has been found 
to make a better growth on ammonium compounds than on 
nitrates. This is a case in which the plant has evidently 
adapted itself to its surroundings, for upland rice presumably 
uses nitrate nitrogen. However, some dry land plants can 
also use ammonia. It. has been found, for instance, that 
peas obtained nitrogen as readily from ammonium salts as 
from sodium nitrate. On the other hand wheat plants, while 
able to secure some nitrogen from ammonia, have been found 
to grow much better when they could obtain nitrates. 

201. Direct utilization of organic nitrogen by crops. — 
One of the early beliefs in regard to plant nutrition was 
that organic matter was directly absorbed by plants and that 













- 






























\fliuf 




I 


Y ' 


L 

f 

/ 


pi .,§ 


g|jN 




: : 


■ ill 


■mm ' ' wKf? 


7 / 




#1 








1 IM^%M 


mm ' 


f-i'I- 1 








?.'ffflnfi f 


' 


■ I .'* 




Hf 5 ^ 


*ij 


L ,,.,, 




"T '^^"^M 




° H 


■ 




1 :•' 


v : -!m* A " |9 "4 




Plate XII. Fertilizer Tests. — Some soils respond best to one 
fertilizer constituent, others to another. Note that the best growth of 
oats in the upper figure is in the vessels that received nitrogen. In the 
lower figure the best growth is in the vessel that received phosphoric acid. 



NITROGENOUS FERTILIZERS 157 

it furnished their chief supply of food. Opinion afterwards 
swung to the opposite extreme, and it was generally held 
that no organic matter is absorbed by agricultural plants. 
Lately, however, it has been shown that many crops can use 
nitrogenous organic matter, and an organic compound called 
creatinin, that has been isolated from soil, was found to 
produce a better growth of wheat seedlings than did sodium 
nitrate. This may account in part for the high fertilizing 
value of farm manure. Many crops, especially among 
garden vegetables, are most successfully grown only when 
supplied with organic nitrogenous materials. 

202. Forms of nitrogen in fertilizers. — There arc many 
different kinds of material used to provide nitrogen in com- 
mercial fertilizers. Their value varies considerably, because 
the nitrogen in some is not so readily available as it is in others. 
In some the nitrogen is in the form of nitrate, in others am- 
monia, but most of the mixed fertilizers contain some or all 
of their nitrogen in the form of organic matter. 

203. Nitrate of soda. — This material is found in natural 
deposits in northern Chili, where it is mined in enormous 
quantities and shipped to most of the European countries 
and to the United States. It is refined before shipment, 
reaching this country nearly 06 percent pure. Between 15 
and 16 percent of the total material is nitrogen. The im- 
purities are not of a kind to be injurious to plants. 

This fertilizer is easily soluble; in water and is readily ab- 
sorbed by most farm crops. It is the most active form of 
nitrogen. Because it does not need to be acted on by soil 
organisms before being used by plants, it is of great value in 
starting growth in the early spring, before the soil is warm 
enough to cause a conversion of the nitrogen of soil organic 
matter, or of farm manure into nitrates. It will be remem- 
bered that nitrates are largely washed out of the soil during 
the fall and winter and that there is not usually enough 



158 



SOILS AND FERTILIZERS 



of this form of nitrogen to start plant growth earry in the 
spring. 

204. Crops markedly benefited by nitrates. — Winter 
grain is usually benefited by an application of 25 to 50 
pounds to the acre of nitrate of soda about the time that 
growth begins in the spring. The phosphoric acid and potash 
fertilizers may be applied in the fall. 

Timothy meadow responds wonderfully to a top dressing 
of nitrate when the plants first show signs of life. Not only 
is the yield of hay increased, but the sod is thickened, which 
increases its value as a manure for succeeding crops. Phos- 
phoric acid and potash fertilizers should be applied at the 
same time. The following table shows the increased yield 
of hay and succeeding grain crops obtained from applications 
of nitrate fertilizer applied only to the grass crops. Note 
the increased yield of hay and grain from larger applications 
of nitrate when the other fertilizers are not increased, and 
also the striking effect of the better sod on the yield of corn, 
which crop was not fertilized. This offers a rational method 
for producing organic manure from mineral fertilizers. 

Table 34. — Yields of Hay and Grain on Unfertilized Soil 
and on Soil Fertilized for Hay but not for Grain 



Plat 
No. 


Pounds Fertilizer per Acre 


Yields of Crops per Acre 


Hay 3 

Years 


Corn 


Oats 


Wheat 


720 
721 

725 
726 


No fertilizer 

f 160 lbs. nitrate of soda 

< 80 lbs. muriate of potash > . . 
[ 320 lbs. acid phosphate J 

f 320 lbs. nitrate of soda 

< 80 lbs. muriate of potash } . . 
[ 320 lbs. acid phosphate J 

No fertilizer 


Tons 

4.5 

8.4 

10.5 

4.2 


Bu. 

35.1 
55.7 

62.9 
33.4 


Bu. 

33.5 

36.4 

38.2 
29.7 


Bu. 

19.3 

18.7 

19.5 

22.8 



NITROGENOUS FERTILIZERS 159 

By the time the wheat crop was raised the beneficial effect 
of the timothy sod had disappeared. 

Many kinds of garden vegetables must have a rapid 
growth in order to have the succulence upon which their 
value largely depends. To secure this quick growth nitrate 
of soda gives an excellent form of nitrogen on account of its 
ready availability. As previously noted, however, it is not 
an adequate substitute for organic nitrogen for all kinds of 
garden crops. 

205. Effect of nitrate of soda on soils. — Nitrates are 
easily leached from soils, and for that reason nitrate of soda 
should not be applied in the autumn as it will be lost, in large 
part, during the fall and winter. Even when applied pre- 
paratory to planting, it should not be used in excessive quan- 
tities at one time, but if large applications are necessary 
apply part after the plants have made some growth. 

It has been found that the continued and abundant use of 
nitrate of soda causes some soils to become deflocculated, 
resulting in a puddled condition when the soil is worked wet 
and a cloddy condition when dry. This, however, is not 
likely to occur with any ordinary use of the fertilizer. On 
acid soils it serves a double purpose, for it tends to correct 
acidity. 

206. Sulfate of ammonia. — The source of supply of this 
fertilizer is coal, which when distilled, as is done in the man- 
ufacture of illuminating gas, or in the production of coke, 
yields among other products ammonia from which sulfate 
of ammonia is made. The industry has grown enormously 
in recent years, but has by no means reached its maximum, 
as of the hundreds of thousands of tons of coal burned an- 
nually for the manufacture of coke in this country barely 
more than one-half is used for the production of ammonia. 
There are still great possibilities for obtaining nitrogen from 
this source. 



160 SOILS AND FERTILIZERS 

207. Composition of sulfate of ammonia. — There is more 
nitrogen in a ton of this fertilizer than in any other. The 
commercial material usually contains about 20 percent of 
nitrogen, which is from eighty to one hundred pounds more 
than is contained in a ton of nitrate of soda. It is easily 
soluble in water, but when applied to soils the ammonia is 
absorbed, and probably very little of it is taken up directly 
by plants. On the other hand, the absorbed ammonia 
nitrifies readily, especially if there is plenty of lime in the 
soil, and the nitrates thus formed may readily be used by 
plants. 

208. Action when applied to soils. — A pound of nitrogen 
in the form of sulfate of ammonia has slightty less value than 
the same quantity in the form of nitrate. If the soil to which 
it is applied is in need of lime, the value of the fertilizer will 
be less than if sufficient lime be present. It also tends to 
make a soil acid when used in large quantities for a long 
period. These two facts make it apparent that lime should 
be abundantly supplied to soils on which this fertilizer is 
used. Lime, whether it is applied to the soil or is naturally 
present, serves to neutralize the acid formed when the am- 
monia is converted into nitric acid by soil bacteria, which is 
the process by which nitrates are formed, and also to neutral- 
ize the sulfuric acid left in the soil when the ammonia is 
changed by this process. 

The nitrates resulting from the fermentation of sulfate of 
ammonia are quickly leached out of the soil when no plants 
are growing on it ; therefore sulfate of ammonia should not 
be applied at that time. In England the following losses 
of nitrogen occurred from plats on which nitrate and am- 
monium salts were used, and on which crops were grown. 
The term " minerals " is here used to mean phosphoric acid 
and potash fertilizers. 



NITROGENOUS FERTILIZERS 



161 



Table 35. — Pounds of Nitrogen in Drainage Water from 
Soil Treated with Nitrate and Ammonia Fertilizers 





1879 


-1880 


1880- 


-1881 


Treatment 


Spring 


Harvest 


Spring 


Harvest 




Sowing 


to 


Sowing 


to 




to 


Spring 


to 


Spring 




Harvest 


Sowing 


Harvest 


Sowing 


Unmanured 


1.7 


10.8 


0.6 


17.1 


Mineral fertilizers only .... 


1.6 


13.3 


0.7 


17.7 


Minerals + 400 pounds ammonium 










salts 


18.3 


12.6 


4.3 


21.4 


Minerals + 550 pounds nitrate of 










soda : 


45.0 


15.6 


15.0 


41.0 


Minerals + 400 pounds ammonium 










salts applied in autumn . . . 


9.6 


59.9 


3.4 


74.9 


400 pounds ammonium salts alone . 


42.9 


14.3 


7.4 


35.2 


400 pounds ammonium salts + sul- 










phate of potash 


19.0 


16.4 


3.7 


25.3 


Estimated drainage in inches . . . 


11.1 


4.7 


1.8 


18.8 



These figures show a very considerable loss of nitrogen 
from the nitrogen-fertilized plats, with a somewhat greater 
loss from the nitrate-treated plats than from those receiv- 
ing ammonia. Neither of these fertilizers is well designed 
to add to the total supply of nitrogen in the soil, for which 
purpose a less easily nitrifiable fertilizer must be used. 

209. Cyanamid. — Within recent years it has been found 
possible to take nitrogen from the atmosphere and combine 
it with lime for use as a fertilizer. Two different materials 
are manufactured. One is called cyanamid, the other 
nitrate of lime. Both are produced by the use of powerful 
currents of electricity, but the processes are essentially dif- 
ferent and only the cyanamid is now being manufactured in 
the United States, and it alone will be discussed in this book. 

210. Composition of cyanamid. — The word cyanamid is 



162 SOILS AND FERTILIZERS 

merely a trade name. Another name that has been used is 
lime nitrogen. The latter is good because it emphasizes the 
fact that the fertilizer contains lime, which is a point in its 
favor, as the lime helps to overcome soil acidity. There is 
about 26 percent of caustic lime in the fertilizer. How- 
ever, in the quantities in which fertilizers are used the 
sweetening effect of the lime would not go very far. The 
fertilizer usually contains between 15 and 16 percent of nitro- 
gen, which puts it on a par with nitrate of soda in this 
respect. 

211. Changes in the soil. — Cyanamid must be decom- 
posed in the soil before its nitrogen becomes available to 
plants. It is, therefore, not as rapid in its effects as is nitrate 
of soda, but resembles sulfate of ammonia in this respect. 

Under some conditions products may be formed during its 
decomposition that are more or less injurious to plants. 
This is said to be true when the fertilizer is incorporated 
with water saturated soil or very acid soil. As decomposi- 
tion proceeds these injurious substances are destroyed. In 
order to be sure that no injury will be done to plants, cyan- 
amid should be applied at least a week before planting. 

It is not well adapted to use on very sandy soils, nor does 
it give its best results when used as a top dressing, as it re- 
quires incorporation with the soil for its proper decomposi- 
tion. Ordinarily its fertilizing value is not greatly below that 
of sodium nitrate, and is about equal to that of sulfate of 
ammonia. 

212. Fertilizers containing organic nitrogen. — There are 
a great many materials containing organic nitrogen that 
are used as fertilizers. As many of them are of little or no 
value for other purposes they would be wasted if not used to 
benefit the land. There is very great diversity as to their 
fertilizer value, but in general the availability of the nitrogen 
to plants is less than that of nitrate of soda. In order that 



NITROGENOUS FERTILIZERS 163 

their nitrogen shall become available, the substances them- 
selves must decompose in the soil, the nitrogen undergoing 
the usual transformations. 

Many of the organic fertilizers contain phosphoric acid, 
or potash, or both. These ingredients add to the value of 
the fertilizer. They will be discussed under the heads of 
(1) vegetable products, (2) animal products, (3) guano. 

213. Vegetable products. — Among these are cottonseed 
meal, linseed meal and castor pomace together with other 
materials that are less used and that will not be discussed 
here. 

The meals here mentioned are primarily stock-foods and 
are more profitably fed to live-stock, the resulting manure 
being applied to the soil, than used directly as fertilizer. 
Nevertheless, cottonseed meal is used extensively as a fer- 
tilizer and linseed meal to a less extent. The former is much 
used for tobacco of better grades and as a top dressing for 
lawn grasses, as it does not have the offensive odor that char- 
acterizes many of the organic fertilizers. 

Cottonseed meal contains between 6 and 7 percent of nitro- 
gen when free from hulls, and 4 percent when these are pres- 
ent. It also contains about 2.5 percent of phosphoric acid 
and 1.5 percent of potash. 

Linseed meal contains about 5.5 percent of nitrogen, and 
between 1 and 2 percent of phosphoric acid and of potash. 

Castor pomace, which is the residue after the extraction 
of castor oil from the beans, has a nitrogen content of between 
5.5 and 6 percent, and a rather variable amount of phos- 
phoric acid and potash. 

214. Animal products. — These include the slaughter house 
products among which are red dried blood, with about 13 
percent of nitrogen ; black dried blood, with 6 to 12 percent 
nitrogen ; dried meat and hoof-meal, with 12 to 13 percent 
nitrogen ; tankage, of which the concentrated product has 



164 SOILS AND FERTILIZERS 

a nitrogen content of from 10 to 12 percent, and crushed 
tankage, that has from 4 to 9 percent nitrogen. Leather 
meal and wool and hair waste may also be mentioned but 
they have only a small fertilizer value. Ground fish or fish 
waste is also sold as a fertilizer and usually contains about 
8 percent of nitrogen. 

Dried blood is the most readily decomposed of these 
products, and its nitrogen is in the most available form. 
It also contains a small quantity of phosphoric acid. It is 
slower in its action than either nitrate of soda or sulfate of 
ammonia. With this, as with all the animal products, the 
soil should be in a condition favorable to decomposition of 
organic matter and to the formation of nitrates. 

Dried meat contains a high percentage of nitrogen, but 
does not decompose so easily as does dried blood, and is not so 
desirable a form of nitrogen. It may be fed to hogs or poultry 
to advantage, and the resulting manure is very high in nitro- 
gen. 

Hoof-and-horn meal is high in nitrogen, but decomposes 
slowly. Its nitrogen is less active than dried blood or meat. 
It is useful to increase the store of nitrogen in a depleted soil. 

Tankage is highly variable in composition. The concen- 
trated tankage, being more finely ground, undergoes more 
readily the decomposition necessary for the utilization of its 
nitrogen. 
. Leather meal and wool and hair waste when untreated 
are in such a tough and undecomposable condition that they 
may remain in the soil for years without losing their structure. 
They are not to be recommended as manures. 

215. Fish waste. — The material sold under this name is 
usually waste from canning factories, and consists of the 
heads, tails, bones, entrails and all other discarded portions 
of the fish that are canned. As a fertilizer it acts very slowly 
and is not at all adapted to crops that make their growth in 



NITROGENOUS FERTILIZERS 165 

the early spring. It is better adapted to sandy soils than to 
heavy ones. 

216. Guano. — This was formerly a very important fer- 
tilizing material, but there is comparatively little of it im- 
ported into this country at present, because the world's 
supply is nearly exhausted. It consists of the excrement and 
carcasses of sea fowl. The composition of guano depends 
on the climate of the region in which it is found. Guano from 
an arid region contains much more nitrogen and potash than 
that from a region of more rainfall, because these constituents 
ha^e been leached out of the latter. All of the plant-food 
materials contained in guano are in a readily available con- 
dition, and its fertilizing value is high. 

217. Effects of nitrogen on plant growth. — The all impor- 
tant part that nitrogen plays in plant growth is that of an 
indispensable constituent of protein, which is the basic sub- 
stance in every cell of every plant. It is therefore concerned 
in the formation of every part of the plant. If the supply 
of nitrogen is inadequate, the effect is to decrease the yield 
of the crop, especially the leaves, stems, stalks or straw, 
while the quantity of grain produced is not curtailed to the 
same extent. On the other hand, an excess of available nitro- 
gen causes an abundant growth of the vegetative parts of the 
plant rather than of the seed or grain. As a result, in 
cereals the straw becomes so long and weak that the plants 
fall down or " lodge." Grass crops are less likely to suffer 
from an excess of nitrogen than are cereals, and nitrogen 
is particularly beneficial to the grasses. Many vegetables 
that are grown for their vegetative parts can utilize to good 
advantage a large quantity of nitrogen. If nitrogen is not 
present in sufficient quantity for cereals, the kernels are 
shriveled and light. There can be no doubt that the lack of a 
readily available supply of nitrogen at critical periods in the 
growth of plants is a frequent cause of curtailed crop yields. 



166 SOILS AND FERTILIZERS 

Another effect of excess nitrogen supply is to delay the 
ripening of crops. This is often seen in orchards that receive 
clean cultivation throughout the summer. The large supply 
of nitrogen thus made available, as well as the moisture re- 
tained in the soil, serves to retard ripening and the immature 
wood is likely to be injured by winter temperatures. In 
regions having short, but usually hot seasons, cereals are 
sometimes delayed in ripening until injured by frost. 

Sometimes the quality of crops may be injured by an ex- 
cess of nitrogen. Barley deteriorates in its malting qualities, 
and peaches in flavor when too much nitrogen is supplied* 

The percentage of nitrogen may be increased in some crops 
by supplying a large quantity of available nitrogen. Tim- 
othy hay responds in this way, as do many vegetables, and the 
straw and even the grain of cereals. 

Resistance to disease is often decreased when nitrogen is 
abundant. This is familiarly exhibited in the ease with which 
a crop of wheat or oats on very rich soil will succumb to rust. 
There are numerous cases of this kind, probably due to a 
change in the physiological resistance of the plant to the 
diseases to which it is exposed. 

218. Availability of nitrogenous fertilizers. — It has been 
pointed out that nitrates are the form in which nitrogen is 
most acceptable to the larger number of agricultural plants, 
and this being the case fertilizers having nitrates offer a very 
readily available form of nitrogen. Ammonium salts not 
being so readily appropriated by most plants require at 
least partial conversion into nitrates. Ammonia is ab- 
sorbed by soil, but in its absorbed condition readily 
undergoes nitrification. However, there is apparently some 
loss or conversion into an insoluble condition, for experiments 
have generally shown that there is rarely quite as much nitro- 
gen recovered by crops from sulfate of ammonia as from ni- 
trate of soda. The organic nitrogenous fertilizers must un- 



NITROGENOUS FERTILIZERS 



167 



dergo ammonification and nitrification in the soil. Some 
of them decompose much more readily than others. 

In order to ascertain the relative degree of availability of 
the nitrogenous fertilizers, experiments have been conducted 
by numerous investigators in which they have used one of 
these fertilizers on one or more plats of land, or in one or more 
vessels of soil, and other nitrogenous fertilizers in a similar 
way. It is, of course, always necessary that there shall be 
an abundance of all the other plant-food materials. These 
experiments were repeated for several years with different 
crops, at the end of which time a comparison was made of the 
yields of the crops on the soil treated with the different fer- 
tilizers. In Table 36 the results of some of these experiments 
are stated, with the yields obtained with nitrate of soda 
taken as 100 in each case. 

Table 36. — Relative Effectiveness of Nitrogenous Ferti- 
lizers 



Nitrogen Carriers 



Nitrate of soda . 
Sulfate of ammonia, 
Dried blood . . 
Bone meal . . . 
Stable manure . 
Tankage .... 
Horn-and-hoof meal 
Linseed meal . . 
Cottonseed meal 
Castor pomace . . 
Wool waste . . . 
Leather meal . . 
Dry ground fish 



Wagner 


Johnson 


AND 


and 


DORSCH 


Others | 


100 


100 


90 




70 


73 


60 


17 


45 






49 


70 


68 




69 




65 




65 


30 




20 






64 



AND 
LlPMAN 



100 
70 

64 

53 



While these experiments are helpful in giving an idea 
of the relative values of these fertilizers, they do not necessa- 



168 SOILS AND FERTILIZERS 

rily hold for every soil. It will be noticed that there is con- 
siderable discrepancy in these results, but that is always to 
be expected. A fertilizer may have a more rapid rate of am- 
monification or nitrification than another fertilizer in one 
soil and less rapid in another soil. 

219. Relative values of organic and inorganic nitrogenous 
fertilizers. — In the experiments cited the organic fertilizers 
were, in every case, less effective than the inorganic ones. 
However, the cost of a pound of nitrogen is generally more in 
the better class of organic fertilizers, like dried blood, than it 
is in the inorganic fertilizers, like nitrate of soda and sulfate 
of ammonia. This may be because of the demand of fer- 
tilizer manufacturers for a dry material for their goods, but 
the beneficial effect of the organic matter it contains may 
also be a factor in creating the demand for dried blood. 

QUESTIONS 

1. Name the forms in which nitrogen occurs in soils. 

2. State what forms of nitrogen are absorbed by crops, and what 
differences exist between plants in this respect. 

3. Name the fertilizer materials that contain nitrogen, and spec- 
ify the form in which nitrogen occurs in each. 

4. What crops are particularly benefited by nitrate fertilizers ? 

5. How is the nitrogen of nitrate and ammonia fertilizers likely 
to be lost from soils, especially if no crop is on the land ? 

6. How may danger arising from formation of poisonous products 
in the decomposition of cyanamid be avoided ? 

7. Describe the effects of nitrogen on plant growth. 

8.' State the order of availability of nitrogen in nitrate of soda, 
sulfate of ammonia and dried blood. 

LABORATORY EXERCISES 

Exercise I. — In Exercise V, Chapter I, an experiment designed 
to show the importance of the plant-food materials to plant growth 
was described. If this test has been properly conducted the influ- 
ence of nitrogen upon plant growth will be clearly shown. 



NITROGENOUS FERTILIZERS 169 

Exercise II. — Examination and identification of nitrogen 
fertilizers. 

Materials. — Set of fertilizers (comprising sodium nitrate, am- 
monium sulfate, cyanamid, dried blood and tankage), evaporating 
dish, phenoldisulphonic acid, ammonia, funnel and filter paper, 
litmus paper, hand lens, flame. 

Procedure. — It is well for the student to be able to identify 
the common fertilizers and to know a few practical tests when the 
identity is in doubt. The following outline is given with this end 
in view. 

Sodium Nitrate 

This fertilizer appears in clouded light yellowish crystals, soluble 
in water and rather deliquescent. It has no marked odor. 

Hold a crystal in the flame. Note the brilliant yellow color. 
This is a test for the element sodium. 

Test for the nitrate part of the fertilizer by moistening a crystal 
in an evaporating dish with a drop of phenoldisulphonic acid. 
Allow to stand a few minutes and then dissolve in a little water. 
Now neutralize with ammonia and obtain the yellow color charac- 
teristic of nitrates. 

Ammonium Sulfate 

This fertilizer is a light grayish colored salt, finely ground and 
soluble in water. Heat a little in an evaporating dish and note the 
odor of ammonia. 

Cyanamid 

Cyanamid is a fine, dry, black powder which carries besides its 
nitrogen compound, carbon and lime. The carbon may be tested 
for by rubbing the fertilizer between the fingers. Dissolve as much 
of the fertilizer as possible in water, filter and test the filtrate with 
litmus paper. It should be intensely alkaline on account of the 
lime it contains. The physical characters of the fertilizer are such 
as to make it easily recognized. 

Dried Blood and Tankage 

These materials can be easily identified and distinguished by 
their physical properties, especially if a hand lens is used. Consid- 
erable hair and bone is likely to be found in tankage. The odor of 
both is characteristic. Study each fertilizer until identification is 
easy. 



170 SOILS AND FERTILIZERS 

Exercise III. — Comparison of fertilizer effects on plant 
growth. 

Materials. — Fertilizers, flower pots, poor sandy soil, oat seed. 

Procedure. — It may be of advantage to compare two or more 
of the nitrogen fertilizers with reference to their effect on plant 
growth. Fill flower pots with the same amount of a poor 
sandy loam after thoroughly mixing the fertilizer with the soil. 
Apply nitrogen fertilizers at the rate of 250 pounds per acre (1 of 
fertilizer to 1 0,000 of soil) . Also add at the same time acid phosphate 
and muriate of potash at the rate of 1 to 5000 of soil respectively. 
One gram of lime per pot is also necessary. Leave one pot untreated 
with the nitrogen fertilizers as a check. Now plant oat seeds and 
bring the soil to optimum moisture content. When seedlings are 
a week old thin to proper number. Keep pots in suitable place and 
observe relative development of the plants under the different treat- 
ments. 



CHAPTER XII 
PHOSPHORIC ACID FERTILIZERS 

Fertilizers commonly used in this country for their phos- 
phoric acid may be divided into two classes, natural phos- 
phate fertilizers and acid phosphate fertilizers. The former 
are in the condition in which they are found in nature, and 
are very difficultly soluble. The latter are merely the phos- 
phate fertilizers that have been treated with strong acid, 
after which process they are readily available to plants. 
There is an intermediate form present in basic slag, which is 
not quite so available as the acid phosphate, but more 
readily available than the natural phosphate fertilizers. 
Natural phosphates, when in organic compounds, like bone, 
are more readily available than when in purely. inorganic 
compounds, like rock. 

220. Bone phosphate. — Most of the bone now used in 
fertilizers has been steamed or boiled, which removes the fat, 
and also the nitrogen that fresh bones contain. Fresh bones 
have a content of about 22 percent phosphoric acid and 
4 percent nitrogen. Steamed bones have from 28 to 30 per- 
cent phosphoric acid and 1.5 percent nitrogen. Bone tankage, 
which has already been spoken of as a nitrogenous fertilizer, 
contains from 7 to 9 percent of phosphoric acid. Bone should 
always be finery ground, as it is then more readily available. 
It is a slow acting form of phosphoric acid. 

221. Mineral phosphates. — These are found as natural 
deposits of rock in various parts of the world, some of the 

171 



172 SOILS AND FERTILIZERS 

most extensive being in the United States. When ground 
these are often called " floats." South Carolina phosphate 
contains from 26 to 28 percent of phosphoric acid. Florida 
phosphate exists in the forms of soft phosphate, pebble phos- 
phate and boulder phosphate. Soft phosphate contains from 
18 to 30 percent phosphoric acid, and because of its being 
more easily ground than most of these rocks it is often applied 
to the land without being first converted into an acid phos- 
phate. The other two forms, pebble phosphate and boulder 
phosphate, are highly variable in composition, varying from 
20 to 40 percent in phosphoric acid content. 

Tennessee phosphate contains from 30 to 35 percent of phos- 
phoric acid. In addition to these deposits, which have been 
extensively mined since their discovery, there have been found 
much larger deposits in the states of Idaho, Wyoming and 
Montana, but these have not yet been worked. 

Apatite and coprolites are other forms of natural phosphate 
that are used as fertilizers. The former is found in Canada 
and the latter in England and France. They are not of much 
importance in the fertilizer business of this country. 

222. Basic slag. — ■ This is also called Thomas phosphate. 
It is a by-product in the manufacture of steel from pig iron 
rich in phosphorus. The phosphoric acid in this material is 
more readily available than that in the mineral phosphates, 
and when used as a fertilizer it does not require treatment 
with acid. It should be finely ground. It is not extensively 
used in the United States. 

223. Acid phosphate. — The very difficultly soluble phos- 
phates may be rendered more easily soluble by treatment 
with sulfuric acid. The product is called acid phosphate. 
When applied to soils it is much more available to plants 
than are any of the natural phosphates. Acid phosphates 
contain gypsum or land plaster as well as phosphoric acid. 
The proportion of the total quantity of phosphoric acid 



PHOSPHORIC ACID FERTILIZERS 173 

originally present that is rendered soluble depends on the 
quantity of sulfuric acid added. In practice there is usually 
part of the phosphoric acid that is left in an insoluble form. 

224. Composition of acid phosphate. — Acid phosphate 
made from animal bone is called dissolved bone and contains 
about 12 percent of available and from 3 to 4 percent of 
insoluble phosphoric acid. It also contains some nitrogen. 
When made from South Carolina rock, acid phosphate con- 
tains from 12 to 14 percent of available phosphoric acid, 
including from 1 to 3 percent of what is called reverted 
phosphoric acid. The best Florida acid phosphate contains 
as high as 17 percent, and the Tennessee acid phosphate 14 
to 18 percent of available phosphoric acid. 

225. Reverted phosphoric acid. — A change sometimes 
occurs in acid phosphate on standing, by which some of the 
phosphoric acid becomes less easily soluble, and to that extent 
the value of the fertilizer is lessened. This change is known 
as reversion. It is much more likely to occur in acid phos- 
phate made from rock than in that made from bone. The 
quality of the material affects this change. The presence of 
iron and aluminum is supposed to increase reversion. Re- 
verted phosphoric acid is probably not so available as the 
original acid phosphate. 

226. Absorption of acid phosphate by soil. — Like many 
soluble substances acid phosphate, when applied to soil, 
is in part absorbed and held in a form in which it will not be 
leached out by the drainage water, but on the other hand, 
remains in a condition in which it is available to plants. 
Part of the soluble phosphoric acid may unite with iron or 
aluminum in the soil to form insoluble combinations. The 
richer a soil is in lime the less is the danger of forming these 
insoluble combinations. The availability of acid phosphate 
may continue for a second year, or even longer, after being 
applied to the soil. 



174 SOILS AND FERTILIZERS 

227. Relative availability of phosphoric acid fertilizers. 

— The availability of these fertilizers has been casually men- 
tioned as each was discussed, but a brief resume will serve 
to make the matter more definite. Acid phosphate, including 
dissolved bone, is the most readily available of the phos- 
phoric acid fertilizers. The reverted portion is more or less 
available, depending on the character of the original rock, 
and on the kind of soil to which it is applied. It is not as 
valuable as the soluble phosphoric acid. The insoluble por- 
tion has no greater availability than the rock from which the 
acid phosphate was made. 

Next to acid phosphate in availability comes basic slag, 
then steamed bone and finally the rock phosphates. 

Acid phosphate and basic slag may be used for top dressing 
grass or winter grains, but the other fertilizers must be in- 
corporated in the soil in order to become available. It is 
necessary that they shall be acted on by the soil water having 
carbon dioxide in solution and possibly by other acids formed 
by the decomposition of organic matter. 

228. Rock phosphate versus acid phosphate. — The ques- 
tion has frequently been raised in the last few years regarding 
the use of ground rock phosphate or floats as a substitute for 
acid phosphate. Which of these practices is the better must 
be largely determined by practical experiment, and by a study 
of the conditions under which floats become available. 

It is urged in favor of floats that the price of phosphoric acid 
is much less in this form than in the form of acid phosphate, 
which is made by a more or less expensive process. It is 
further argued that even if much more material must be used 
in order to get a pound of available phosphoric acid the re- 
mainder stays in the soil to increase the total supply, and that 
gradually it will become available, finally perhaps reaching 
a point where no more need be applied. 

On the other side is the well-established practice of using 



PHOSPHORIC ACID FERTILIZERS 175 

acid phosphate, which dates back more than half a century, 
and has been accepted during that time as an improvement 
over the use of untreated bone, which was largely super- 
seded when the. process of making acid phosphate was in- 
vented. 

On most soils acid phosphate apparently gives the more 
profitable immediate returns. On some of the rich soils of 
the Middle West, however, there is an indication that 
ground rock is a more economical source of phosphoric acid. 
Except in those regions where the superiority of floats has 
been demonstrated it is probably safer to use acid phosphate. 

229. Effect of phosphoric acid on plant growth. — As has 
been previously stated, phosphoric acid is essential to the 
growth of plants. It is absorbed by plants at a fairly uniform 
rate throughout the period of their active growth, while nitro- 
gen is largely taken up during the early stages of growth. 
Nitrogen and phosphoric acid are closely associated in plant 
development. 

One very apparent effect of phosphoric acid is to hasten 
ripening. Cereal plants that receive an ample supply of 
available phosphoric acid reach the heading stage and final 
maturity sooner than do plants having an insufficient supply. 
This may be an advantage in a climate having a cool short 
season as it may help the crop to avoid frost in the fall. On 
the other hand this rapid ripening may limit the yield 
in a dry season, when there is a tendency for the crop to 
shorten its growing periods sufficiently to curtail the quan- 
tity of nutrients it absorbs and the food it elaborates. 

Root development is always stimulated by available phos- 
phoric acid. Young plants send their roots more deeply 
into the soil, which is an advantage in dry regions, where the 
top soil dries out quickly. Under any circumstances it in- 
creases the absorbing surfaces and benefits growth. 

The quality of many crops, particularly of pastures, is 
improved by phosphoric acid. Animals reared on pastures 



176 SOILS AND FERTILIZERS 

fertilized with phosphoric acid have been found, in a number 
of experiments conducted in Great Britain, to be more vigor- 
ous and to develop faster than when no phosphoric acid was 
applied. 

By balancing the effect of nitrogen, phosphoric acid pre- 
vents an undue formation of straw, at the same time making 
it stronger ; on the other hand, it increases the production of 
grain in cereal crops. In the same way it increases resistance 
to disease, probably by producing a more normal develop- 
ment of the plant cells. 

An insufficient supply of phosphoric acid is less easy to de- 
tect than is an inadequate supply of nitrogen, because its ef- 
fect is exercised on the production of grain or other seeds, 
rather than on the height and color of the plants. It re- 
quires some care, therefore, to detect a lack of phosphoric 
acid. 

230. Plants particularly benefited by phosphoric acid. — 
The crops that respond particularly well to applications of 
phosphoric acid are turnips, barley, cabbage and other plants 
of that family, beets, spinach, radishes and lettuce. Corn is 
said to be well qualified to secure its phosphoric acid from the 
natural phosphates, as are also some of the legumes. 

QUESTIONS 

1. Name the natural phosphate fertilizers. 

2. Why should natural phosphates be finely ground, when ap- 
plied to the soil ? 

3. How does basic slag compare in availability with rock phos- 
phate ? 

4. How is acid phosphate made, and how does it compare 
in availability with the natural phosphates ? 

5. What is reverted phosphoric acid ? 

6. Why is soluble phosphoric acid not readily leached out of soil 
after being applied as a fertilizer ? 

7. What phosphoric acid fertilizers may be used for top dressing 
grass or other crops ? 



PHOSPHORIC ACID FERTILIZERS 177 

8. Compare floats and acid phosphate as sources of phosphoric 
acid when fertilizing land. 

9. Describe the effects of phosphoric acid on plant growth. 

10. Name the plants that are particularly benefited by fertili- 
zation with phosphoric acid. 

LABORATORY EXERCISES 

Exercise I. — In Exercise V, Chapter I, an experiment was 
described that was designed to show the importance of some plant- 
food materials to plant growth. If this test has been properly con- 
ducted it should now be ready to show the actual effects of the 
phosphoric acid on crop development. 

Exercise II. — Examination and identification of phosphate 
fertilizers. 

Materials. — Set of fertilizers (consisting of ground bone, raw 
rock phosphate, basic slag and acid phosphate), hydrochloric acid, 
nitric acid, litmus paper, flame, test tubes, funnel and filter paper, 
ammonium molybdate solution. 

The ammonium molybdate solution is made as follows : 
Dilute 50 c.c. of ammonia (sp. gr. .9) with 75 c.c. of distilled water. 
Dissolve in this 25 grams of molybdic acid. Pour this into a solu- 
tion consisting of 175 c.c. of nitric acid (sp. gr. 1.42) diluted with 
250 c.c. of water. Make the addition slowly with constant stirring. 
Allow to stand in a warm place for two days and then decant the 
clear supernatant liquid for use. 

Procedure. — The fertilizers should be tested as described below 
and examined until their identification is easy and positive. 

Ground Bone 
Bone is usually ground to a coarse powder. It is dry and has a 
decided and characteristic odor. It is light gray in color, insoluble 
in water and has a characteristic appearance under the hand lens. 
Its physical characters are sufficient for identification. 

Ground Phosphate Rock 

Floats appear on the market as a light gray powder, insoluble 
in water and with little odor. 

Dissolve a small amount in hydrochloric acid, heat and filter. Add 
ammonia until a precipitate appears. Dissolve it with a small 
amount of nitric acid. Then add ammonium molybdate. Heat gen- 
tly. A yellow precipitate indicates the presence of phosphoric acid. 

N 



178 SOILS AND FERTILIZERS 

Basic Slag 

This form of phosphoric acid appears as a dry, dark gray powder 
with a slight odor. If differs from eyanamid in that it does not 
stain the fingers upon handling. It is alkaline to litmus paper. 

Test for phosphates as under phosphate rock. 

Acid Phosphate 

This fertilizer is a slightly deliquescent salt, brownish gray in 
color, and finely ground. Its odor is characteristic and serves to 
distinguish it from ground rock. Unlike floats it is partially soluble 
in water. 

Dissolve a small amount in water. Filter and test the filtrate for 
phosphoric acid as described above. 

Exercise III. — Comparison of fertilizer effects on plant 
growth. 

Materials. — Fertilizers, flower pots, poor sandy soil, oat seed. 

Procedure. — The comparison of the various phosphorus fer- 
tilizers upon crop growth, especially acid phosphate and raw rock, is 
a valuable experiment. Fill the required number of flower pots 
with the same amount of a poor sandy loam after thoroughly 
mixing the fertilizer with the soil. Apply the phosphorus ferti- 
lizers at the rate of 250 pounds per acre (1 of fertilizer to 10,000 
of soil). Also add at the same time sodium nitrate and muriate 
of potash at the rate of 1 of fertilizer to 5000 of soil respectively. 
Apply one gram of lime per pot. Leave one pot untreated with the 
phosphorus fertilizers as a check. 

Now plant the oat seed and raise the soil to optimum moisture. 
When seedlings are a week old, thin to required number. Keep 
pots under suitable conditions and observe relative development of 
the various treatments. 



CHAPTER XIII 
POTASH AND SULFUR FERTILIZERS 

The materials used as potash fertilizers, with a very 
few exceptions, are soluble in water. The matter of their 
relative availability is, therefore, of minor importance. 
When applied to soil, the potash salts are absorbed and held 
in a condition in which they leach out only in moderate quan- 
tities, but to a greater extent than does phosphoric acid. In 
the absorbed condition, however, they are readily available 
to plants. 

It seems strange that with the many thousand pounds of 
potash contained in an acre of ordinary land, as may be 
seen by consulting Table 17, there should be any benefit 
derived from the few pounds of potash that are contained 
in a fertilizer. The fact that the fertilizer is effective gives 
emphasis to two facts : (1) the great insolubility of the 
soil potash ; (2) the availability of the absorbed potash. 

231. Stassfurt salts. — Most of the potash fertilizers used 
in the United States come from Germany, where there are 
extensive beds varying from 50 to 150 feet in thickness, lying 
under a region of country extending from the Harz mountains 
to the Elbe river and known as the Stassfurt deposits. 

There are two forms in which potash is found in the Stass- 
furt beds. These are the sulfate of potash and the muriate 
of potash. It is necessary to distinguish between these two 
because the muriate, when used in large applications, has an 
injurious effect on certain crops, among which are tobacco, 

179 



180 SOILS AND FERTILIZERS 

sugar beets and potatoes. On cereals, legumes and grasses 
the muriate may be used without causing any injury, provided 
it is not brought in contact with the seed. 

Comparatively pure forms of both muriate and sulfate of 
potash are on the market. The former contains about 50 
percent of potash, and the latter about 48 to 50 percent. The 
sulfate is more expensive, but the muriate is equally good, 
except on the rather small number of crops that are injured 
by it. 

The mineral produced in largest quantity by the Stass- 
furt mines is kainit, consisting of sulfate of potash and 
muriate of magnesia. It contains from 12 to 20 percent 
of potash. It has the same effect on crops as has the muri- 
ate of potash. 

Kainit should not be drilled with the seed of any crop 
for when placed in direct contact with the seed injury 
may result. It is a wise precaution to apply the kainit a 
week or more before planting, if a heavy application is to 
be made. * 

232. Wood ashes. — The principal supply of potash in this 
country at one time was wood ashes. With the diminished 
consumption of wood as fuel, this source of potash has fallen 
off. Now wood ashes are only an occasional supply. In 
addition to potash, wood ashes furnish considerable lime and 
a little phosphoric acid. There is no muriate present and 
hence no injurious effect on plants, but it should not be 
brought directly in contact with seeds. 

Unleached wood ashes contain 5 to 6 percent of potash, 
• 2 percent of phosphoric acid and 30 percent of lime. Leached 
wood ash^s have only about 1 percent of potash, 1^ percent 
of phosphoric acid and 28 to 29 percent of lime. The un- 
leached ashes are the more valuable. 

Wood ashes are not only an excellent potash fertilizer, 
but are also useful to counteract acidity in soils, for which 



POTASH AND SULFUR FERTILIZERS 181 

purpose the lime in the ashes is even more effective than the 
potash because there is more of it. 

233. Insoluble potash fertilizers. — Many rocks contain 
potash ; for this reason there is a large quantity in soils. It 
has been proposed to grind the rocks that are richest in pot- 
ash and to use them for fertilizer. Experiments with finely 
ground feldspar have been conducted by a number of investi- 
gators, but have given little encouragement for the successful 
use of this material. An insoluble form of potash is not 
given any value in the rating of a fertilizer. 

234. Effects of potash on plant growth. — Plants require 
potash in order to make a normal growth. If no available 
potash is present, the elaboration of sugar and starch in 
plants is curtailed. Crops like potatoes and sugar beets, that 
produce much starch and sugar, are greatly benefited by an 
abundant supply of potash. It also has other functions in 
plants that make it indispensable. The grain of cereals fills 
out better and weighs more to the bushel and the straw is 
stronger, when a good supply of potash is available. Leg- 
umes are usually greatly benefited by potash. The large 
formation of sugar and starch affords the nitrogen-fixing 
bacteria the kind of food which they need, and to obtain 
which they live in symbiosis with the legume. If part of 
a clover and timothy field be well fertilized with potash, 
and another part receive none, it is likely to be the case that 
the proportion of clover to timothy will be much greater on 
the fertilized part of the field than on the unfertilized part, 
unless the natural supply of available potash is unusually 
large. 

Potash tends to delay ripening of plants, but not to the 
same extent as does nitrogen. It also has an influence 
similar to that of phosphoric acid, in that it helps to overcome 
the tendency of nitrogen to make plants less resistant to dis- 
ease. 



182 SOILS AND FERTILIZERS 

235. Sulfur as a fertilizer. — It has been pointed out that 
sulfur is one of the substances essential to plant growth, 
but it has generally been considered that a sufficient quantity 
is contained in arable soils to supply the needs of crops, 
and that its application as a fertilizer is unnecessary. In 
spite of this there have been occasional experiments con- 
ducted from time to time in which sulfur, usually in the form 
of flowers of sulfur, has been applied to soils to ascertain its 
effect on plant growth. 

236. Experiments with sulfur as a fertilizer. — Most of 
the experiments with sulfur have been conducted in Europe. 
In some cases the application of sulfur to the soil was found to 
be beneficial to plant growth, in other cases there was no ef- 
fect. Where no result was produced, it is reasonable to be- 
lieve that there was sufficient sulfur in the soil to supply 
the needs of the plants, and that any further addition was un- 
necessary. In those experiments in which sulfur was found 
to exert a beneficial action we cannot be certain that the in- 
creased plant growth was due to the larger quantity of sulfur 
obtained by the plants. Sulfur has been found to influence 
the action of the germs in soils, and it is possible that the 
plants grew better because the soil nitrogen was converted 
more rapidly into an available form by the stimulating ef- 
fect of sulfur on the bacteria concerned in that process. Sul- 
fur sometimes has other beneficial effects on plant growth. 
These secondary reactions sometimes lead to erroneous con- 
clusions regarding the effect of a fertilizer. 

237. Quantity of sulfur contained in crops. — It has been 
computed from the analyses of various plants that the 
quantity of sulfur, when figured as sulfur trioxide, that is 
removed from the soil by crops of ordinary size is sometimes 
greater, and sometimes less, depending on the kind of crop, 
than is the quantity of phosphoric acid removed by the same 
crop. This may be seen in the following table. 



POTASH AND SULFUR FERTILIZERS 



183 



Table 37. — Pounds of Sulfur Trioxide and Phosphoric Acid 
Removed from an Acre of Soil by Average Crops 



Crop and Yield to the Acre 



Content in Pounds to the 
Acre 



Wheat (30 bu.) 

Barley (40 bu.) 

Oats (45 bu.) 

Corn (30 bu.) 

Alfalfa (9000 lb. dry wt.) . 
Turnips (4657 lb. dry wt.) . 
Cabbage (4800 lb. dry wt.) . 
Potatoes (3360 lb. dry wt.) . 
Meadow hay (2822 lb. dry wt.) 




21.1 
20.7 
19.7 
18.0 
39.9 
33.1 
61.0 
21.5 
12.3 



238. Quantities of sulfur in soils. — Analyses of virgin 
and cultivated soils have shown that there has been a de- 
pletion of sulfur in cropped soils. It also appears that the 
quantity of sulfur trioxide is probably not greater than the 
quantity of phosphoric acid in many soils, as may be seen 
from the following table, which is based on the analyses of a 
considerable number of soils. 

Table 38. — "Pounds of Sulfur Trioxide and Phosphoric Acid 
in Sandy and Clay Soils 



Sandy soils 
Clay soils . 



Pounds per Acre 



Sulfur Trioxide 



1650 
2250 



Phosphoric Acid 



2610 
4230 



239. Quantities of sulfur in drainage water. — Sulfur 
suffers a much greater removal in drainage water than does 
phosphoric acid. In lysimeter experiments this has been 



184 



SOILS AND FERTILIZERS 



shown to amount to from 31 to 56 pounds to an acre in one 
year, depending on whether the soil was limed or unlimed, 
cropped or bare, as shown in the following table. 



Table 39. — Pounds of Sulfur in Drainage Water from One 
Acre of Soil 









Sulfur 




Treatment 


Crops Grown 


(Pounds per 

Acre) 


Lime 


Fertilizer 


1910 


1911 


1912 


1913-14 


1911- 
14 


Annual 
Aver- 
age 


None 


None 


Maize 


Oats 


Wheat 


Timothy 


127.2 


31.8 


None 


None 


None 


None 


None 


None 


176.1 


44.0 


None 


None 


Maize 


Oats 


Wheat 


Timothy and clover 


126.2 


31.5 


None 


None 


Maize 


Oats 


Grasses 


Grasses 


172.8 


43.2 


Lime 


None 


Maize 


Oats 


Wheat 


Timothy 


175.7 


43.9 


Lime 


None 


None 


None 


None 


None 


212.6 


53.1 


Lime 


None 


Maize 


Oats 


Wheat 


Timothv and clover 


164.2 


41.0 


Lime 


None 


, Maize 


Oats 


Grasses 


Grasses 


151.0 


37.7 


None 


Sulfate of potash 


Maize 


Oats 


Wheat 


Timothy 


225.7 


56.4 


Lime 


Sulfate of potash 


Maize 


Oats 


Wheat 


Timothy 


248.1 


62.0 



With the rather large removal of sulfur in crops and drain- 
age water, and a somewhat meager supply in the soil, it would 
appear likely that a deficiency might ultimately arise if there 
were no way in which sulfur could be added fo soils. To 
offset the loss there is a certain quantity of sulfur, amounting 
to 6 or 8 pounds an acre, washed down by the rainfall each 
year. There is also a variable quantity of sulfur contained 
in some of the commonly used fertilizers. 

240. Sulfur contained in fertilizers. — It has been rather 
fortunate perhaps that many of the fertilizers that are used 
because they .contain other plant-food materials, also con- 
tain sulfur. This is true of farm manure and other animal 
and bird excrements, residues of crops, animal offal, gypsum 
or land plaster, acid phosphate, sulfate of ammonia, kainit, 
sulfate of potash and all the slaughter house products. 



POTASH AND SULFUR FERTILIZERS 185 

Whether, under ordinary methods of farming, it is desir- 
able to use any fertilizer for the sulfur it contains has not yet 
been ascertained. It would appear, however, to be a subject 
worthy of consideration. 

QUESTIONS 

1. What occurs to a soluble potash fertilizer when applied to 
soil ? 

2. With thousands of pounds of potash in an acre of soil, why 
do a few pounds of fertilizer increase the supply available to plants ? 

3. Where are most of the potash fertilizers obtained? 

4. Name the potash fertilizers. 

5. Describe the effects of potash on plant growth. 

6. Name some crops that are particularly benefited by potash. 

7. Is there any indication that the use of sulfur as a fertilizer 
may be desirable ? 

8. In what manures and fertilizers is sulfur contained ? 

LABORATORY EXERCISES 

Exercise I. — In Exercise V, Chapter I, an experiment designed 
to show the importance of three plant-food materials to plant 
growth was described. If this test has been properly carried out it 
should now be available to show the effects of potash on plant de- 
velopment. 

Exercise II. — Examination and identification of potash fer- 
tilizers and sulfur. 

Materials. — Set of fertilizers (consisting of muriate of potash, 
sulfate of potash, wood ashes and sulfur), nitric acid, hydrochloric 
acid, silver nitrate, filter paper and funnel, flame, litmus paper. 

Procedure. — The fertilizers should be studied and tested until 
identification is sure. 

Muriate of Potash 

This salt is placed on the market as opaque crystals, soluble in 
water. 

Dissolve a small portion of the fertilizer in water and filter. 
Add a drop of nitric acid and then silver nitrate. A white curdy 
precipitate indicates the presence of muriate. 



186 SOILS AND FERTILIZERS 

Sulfate of Potash 

This salt appears as a light yellowish powder, soluble in water and 
non-deliquescent. 

Dip a crystal in hydrochloric acid and then place in the flame. 
The violet color is a test for potash. 

Wood Ashes 

Wood ashes are so characteristic as to need but little description. 
Leach a small portion with water and test the percolate with litmus 
paper. 

Sulfur 

Sulfur is a yellowish gray powder. It melts readily and burns 
with a bluish flame, giving a characteristic odor. It is insoluble in 
water. 

Exercise III. — Comparison of fertilizer effects on plant 
growth. 

Materials. — Fertilizers, flower pots, poor sandy soil, oat seed. 

Procedure. — The study of the effect of the various potash fer- 
tilizers as well as of sulfur might be of value. Fill the required 
number of flower pots with the same quantity of a poor sandy loam 
after thoroughly mixing the fertilizer with the soil. 

If the effects of the various potash fertilizers are to be compared 
add them respectively at the rate of 250 pounds per acre (1 of fer- 
tilizer to 10,000 of soil). Apply at same time sodium nitrate and 
acid phosphate at the rate of 1 of fertilizer to 5000 of soil respec- 
tively. Add one gram of lime to each pot. Leave one pot un- 
treated with potash fertilizers as a check. 

If sulfur is to be used apply it at the rate of 250 pounds per acre. 
Leave one pot with no treatment, have one to which only sulfur is 
applied, prepare a third with a complete fertilizer only (mixture 
of equal parts of sodium nitrate, acid phosphate and sulfate of 
potash applied at the rate of 1 of fertilizer mixture to 5000 of soil), 
and a fourth pot with sulfur plus the complete fertilizer. 

Carry out the experiment as explained in Exercise III, Chapter 
XI, and observe results. 



CHAPTER XIV 
LIME 

In the chapter on acid soils, reference was made to lime 
as a corrective of acidity. Lime is not a, fertilizer in the 
same sense as are the substances that have been discussed 
in the last three chapters. It is, to be sure, an indispensable 
ingredient of plant tissue, but as it is generally present in 
sufficient quantity in arable soils, and as it is rather soluble, 
there is usually enough lime to fully supply plant growth, and 
this in spite of the fact that the soil may be greatly in need 
of liming. It is because of its effect on the soil, rather than 
directly on the plant, that lime is used as a soil amendment. 

241. Forms of lime. -*- The forms in which lime is used 
on soils are (1) ground limestone, (2) marl, (3) air-slaked 
lime, (4) quick-lime and (5) water-slaked lime. The first 
three of these are similar in their effects, and are chemically 
alike, being what is termed carbonate of lime. Quick-lime 
and water-slaked lime have much the same action on soils, 
and are called caustic lime. 

Quick-lime is made by burning limestone in a kiln. Quick- 
lime, when treated with water, forms water-slaked lime. 
Air-slaked lime is quick-lime that has been exposed to dry 
air until it has lost its caustic properties. Marl is found in 
beds in the earth, as is limestone, but it is softer than lime- 
stone. Like limestone it is ground before being used. 

Owing to the combinations of the lime itself with water 
and gases in these various forms, there is required a greater 
weight of some forms than of others to give the same quantity 

187 



188 SOILS AND FERTILIZERS 

of lime. When the materials are fairly pure, the number of 
pounds of each required to give approximately equivalent 
quantities of lime are as follows : 

Quick-lime 56 pounds 

Water-slaked lime •• 74 pounds 

Air-slaked lime, marl, ground limestone . 100 pounds 

When applying lime to land, these relationships should be 
kept in mind. If it is a question of using quick-lime or ground 
limestone one must provide nearly twice as much limestone 
as quick-lime in order to apply an equal quantity of lime. 

242. Absorption of lime by soils. — In the forms in which 
it is applied to soils, lime is not so soluble as potash fertilizers. 
When brought in contact with soil, the lime is absorbed and 
rendered still less soluble. It is, however, somewhat more 
soluble than soil potash, and drainage waters usually con- 
tain several times as much lime as potash. It is the soluble 
part of the lime that has the beneficial effect on crops and 
soils. The ways in which the benefit accrues are numerous 
and will be described in a number of the following para- 
graphs. Lime is usually applied in much greater quantities 
than are fertilizers, but the treatment is given only at inter- 
vals of four or five years. 

243. Lime requirement of soils. — It is possible, by means 
of chemical methods, to ascertain how much lime a soil will 
absorb before it shows alkalinity due to the presence of an 
excess. Such a test is useful to indicate the quantity of lime 
that should be applied to a soil in order that it shall be at 
least temporarily adapted to the production of lime-loving 
plants. 

The results of such a test are usually expressed in pounds 
of lime required to satisfy the absorptive properties of a 
certain number of pounds of soil, as for instance, 2,000,000 
pounds. This will vary in different soils from none to several 
thousand pounds. 



LIME 



189 



244. Effect of lime on tilth. — A clay or loam soil when in 
acid condition tends to become compact and difficult to till. 
The addition of lime to soil helps to bring about a granular 
formation of the small particles, and to give the soil better 
tilth. This effect has previously been noted in § 46. 

245. Effect of lime on bacterial action. — Some of the 
most beneficial bacteriological processes are greatly favored 
by an abundant supply of lime in the soil. Important among 
these are the various processes involved in the formation 
of nitrates from organic forms of nitrogen. It seems also 
to be associated with the operation by which some legumes, 
for instance alfalfa, secure nitrogen from the air. The in- 
creased supply of easily available nitrogen is often reflected 
in the yield and nitrogen content of the crops, as well as in 
the percentage of nitrates in the soil. This is illustrated by 
an experiment in which alfalfa was raised on plats of land 
one of which was limed liberally and the other not limed. 
The hay was weighed when cut, and was then analyzed, 
as were also the weeds growing with the alfalfa. The soil 
was sampled and the nitrates determined. The soil was also 
allowed to stand for ten days at an optimum water content 
and a temperature suited to the production of nitrates, 
at the end of which time the quantities of nitrates formed 
were determined. The results are shown in Table 40. 

Table 40. — The Effect of Liming Soil on the Yield and 
Composition of Alfalfa Raised on It, and on Its Nitri- 
fying Power 





Limed 


Not Limed 


Yield of hay, pounds on plat .... 


103 


75 


Percentage of protein in alfalfa .... 


20.63 


15.88 


Percentage of protein in weeds .... 


10.67 


8.79 


Nitrates in dry soil, parts per million 


8.10 


4.30 


Nitrates produced in ten days, " . . 


176.00 


92.00 



190 SOILS AND FERTILIZERS 

The effect of the lime was not only to increase the yield of 
alfalfa hay, but also its protein content, as well as that of the 
weeds growing with it. The rate of nitrate formation in the 
soil was also greater when limed. 

246. Liberation of plant-food materials. — It has gen- 
erally been held that the application of lime to soils renders 
some of the other plant nutrients more soluble by reason 
of the exchange of lime for these substances in the insoluble 
combinations found in soils. This has been discussed in 
section 115. There is little doubt that magnesia is thus 
rendered more available, but magnesia is rarely lacking. 
Potash is often said to be made soluble, but although such may 
be the case with some soils it is probably not true of all, and 
there is really little evidence to substantiate the claim in any 
case. The use of lime, under some soil conditions, may render 
phosphoric acid more available, probably by supplying a base 
more soluble than iron or alumina, with which, in soils defi- 
cient in lime, the phosphoric acid might otherwise be combined. 

247. Effect on plant diseases. — The presence of abun- 
dance of lime retards the development of certain plant diseases, 
such as the " finger-and-toe " disease to which cabbages 
and some root crops are subject. On the other hand, it 
may promote some diseases, as, for example, potato scab. 

248. The use of magnesian limes. — Some limestone 
contains a considerable proportion of magnesia. When 
grown in water cultures, many agricultural plants are injured 
when the proportion of magnesia is greater than that of 
lime. In soil, however, magnesia is not nearly as soluble 
as lime and consequently there may be many times more 
magnesia than lime present without as much actually being 
in solution. Hence it is seldom that magnesia is injurious, 
and magnesian lime may be used to overcome soil acidity 
except possibly in the few soils in which the ratio of magnesia 
to lime is already very high. 



LIME 



191 



249. Caustic lime versus ground limestone. — As lime 
helps to correct soil acidity no matter in what form it is 
applied, there is little advantage in one form over another 
so long as it is remembered that 100 pounds of ground lime- 
stone are equivalent to 56 pounds of freshly burnt lime, and 
provided the cost, hauling included, is in that ratio. The 
greater ease with which ground limestone may be handled 
would, under these circumstances, give it the preference. 

In respect to its effect on tilth, lime, in the caustic form, 
is apparently more effective than when in the form of ground 
limestone. For heavy clay soil, the compact and cloddy 
condition of which presents a serious difficulty, caustic lime 
is preferable. A comparison of these two forms of lime on a 
heavy clay soil is shown in the following table in which the 
average percentage increase in crops from the limed over the 
unlimed plats for a period of five years is stated. 

• 
Table 41. — Average Percentage Increase in Yield Due to 
Caustic Lime and Ground Limestone 



Form of Lime Applied 



Caustic lime 

Ground limestone . . 

Caustic lime 

Ground limestone . . . . 
Caustic magnesian lime . . 
Ground magnesian limestone 



Pounds 
Applied 
per Acre 



3000 
6000 
1000 
2000 
2000 
3225 



Percentage 

Increase in 

Yield of 

Crops 



20.9 
14.8 
3.9 
3.7 
6.7 
3.3 



250. Fineness of grinding limestone. — The greater 
solubility of finely ground material, as compared with coarse, 
makes it desirable that limestone be at least fairly well 
pulverized before it is used. If it is so ground that all of the 
particles will pass through a sieve having 50 meshes to the 



192 SOILS AND FERTILIZERS 

inch, it will probably be just as effective as if ground much 
finer. 

251. Gypsum or land plaster. — In the early agriculture 
of this country, before ordinary commercial fertilizers were 
used, gypsum was a popular soil amendment. Its effective- 
ness has apparently decreased as the soils on which it was 
used have been longer under cultivation. It has generally 
been credited with liberating potash, and possibly as the 
soils have become more acid it has been less effective in this 
respect. At any rate, it is rarely used at present. 

Gypsum has little effect on tilth and is not in any sense 
a substitute for caustic lime for that purpose, nor is it of 
any value to overcome soil acidity, as it contains a strong 
acid. 

QUESTIONS 

1. How does the need of % a soil for lime differ, in principle, from 
its need for the other fertilizers we have studied ? 

2. Name the forms in which lime is applied to soils. 

3. Which of these are similar chemically and in their effect on 
soils ? 

4. How is quick-lime made «* Water-slaked lime ? Air-slacked 
lime? 

5. How does the solubility of lime compare with that of potash, 
when both are absorbed by soil ? 

6. What is shown by a chemical determination of the lime 
requirement of a soil ? 

7. What is the effect of lime on some of the bacteriological pro- 
cesses in soil ? 

8. How does lime affect the availability of certain other plant 
nutrients in soil ? 

9. What is its effect on certain plant diseases ? 

10. Discuss the use of magnesian limes. 

11. Discuss the use of caustic lime as compared with ground 
limestone. 

12. How does the fineness of grinding limestone affect its imme- 
diate usefulness ? 

13. How does gypsum affect soil ? 



LIME 193 

LABORATORY EXERCISES 

Exercise I. — A study of the forms of lime. 

Materials. — Set of lime samples (ground limestone, marl, quick- 
lime, hydrate of lime and gypsum), hand lens, muriatic acid, litmus 
paper. 

Procedure. — Study the various forms of lime until identifica- 
tion is easy. 

Ground Limestone and Marl 

Ground limestone can be detected by its physical condition, es- 
pecially if a hand lens is used. It is practically insoluble in water. 
Its color varies from white to gray. The presence of carbonates 
may be detected by a few drops of dilute muriatic acid. 

Marl is a soft powdery form of calcium carbonate. Its texture 
and the presence of shells and organic matter serve to distinguish 
it from ground limestone. 

Quick-lime 

Quick-lime appears on the market either in lumps or as a fine 
powder. It is very caustic and intensely alkaline to litmus paper. 
When in contact with water it heats and slakes, becoming hydrate 
of lime. This characteristic distinguishes it from the other forms 
of lime. 

Hydrate of Lime 

This form of lime is a white powder, soluble in water. Its sour 
taste serves to distinguish it from marl and limestone. It is alka- 
line to litmus paper. 

Gypsum 

This amendment is marketed as a grayish to white powder, in- 
soluble in water. It is calcium sulfate. It does not react with acid 
as does the limestone nor with water as does the lump lime. Its 
lack of taste distinguishes it from hydrate of lime. 

Exercise II. — Fineness of ground limestone. 

Materials. — Samples of limestone, 10, 20, 40, 60 and 100 mesh 
sieves, balance and weights. 

Procedure. — The fineness of ground limestone has a marked 
effect on its value. Weigh out 100-gram portions of the various 
samples of limestone and pass them through the sieves. Weigh 
o 



194 SOILS AND FERTILIZERS 

the resulting grades and calculate the proportion of the original 
sample passing through the different mesh sieves. Try to make a 
relative estimate of the value of the various samples on this basis. 

Exercise III. — Effect of lime on biological action. 

Materials. — An acid soil from under sod, two 8-ounce, wide- 
mouth bottles, hydrate of lime, large vessel for mixing soil and 
water, funnel and filter paper, evaporating dishes, water bath, 
phenoldisulphonic acid, ammonia, flame, two 100 c.c. graduated 
cylinders. 

Procedure. — Place 50-gram samples of the acid soil in each of 
two 8-ounce bottles. Add and mix well with one gram of carbonate 
of lime. Bring the soils in each bottle up to optimum moisture 
content. Plug mouths lightly with cotton and set aside at opti- 
mum temperature for a week. 

Now estimate nitrates in manner described in Exercise I, Chap- 
ter IX. A comparison of the results will show the influence of lime 
on nitrification. Apply these results to practical problems. 

Exercise IV. — Flocculation by lime. 

Materials. — Ground limestones and hydrate of lime ; large 
bottle for preparing soil suspension, two 100 c.c. graduated cylinders. 

Procedure. — Prepare a soil suspension by shaking a heavy 
clay soil for 15 minutes in a bottle partially filled with water (one 
of soil to ten of water) after adding a few drops of strong ammonia. 
Allow to stand for two or three hours and then pour suspension into 
the cylinders. Fill to 100 mark. Now add to one a pinch of hy- 
drate of lime and to the other the same amount of ground lime- 
stone. Shake well and allow to stand. 

Watch closely and explain results. Apply the principle involved 
here to actual field practice. 

Exercise V. — Flocculation by lime. 

Materials. — Clay soil and hydrate of lime. 

Procedure. — Prepare from one portion of clay soil a well-puddled 
ball. Add hydrate of lime to another portion of the clay soil (rate, 
1 of lime to 500 of soil), and work into a ball after adding sufficient 
water. Allow the two samples to dry thoroughly. Crush each one. 
Note difference in crushing resistance and the structural character 
of each soil. Apply results to actual field practice. 

Exercise VI. — Lime and the rotation. 

The place of lime in a rotation depends on a number of factors. 
Discuss these with the student. Take a number of standard rota- 



LIME 195 

tions and decide where in the rotation the lime should come and 
why. 

Encourage the pupils to obtain the rotations used on their home 
farms and discuss lime in relation to such rotations. It might also 
be well to visit some good farmer and discuss with him the form of 
lime he buys, how he applies it, what amounts he uses and where in 
the rotation he adds it to the soil. The practical phases of the use 
of lime are what the pupil should understand. 

Exercise VII. — Problems — Forms of lime to apply. 

In buying lime the form that will give the greatest amount of 
calcium for the money is usually purchased unless the flocculating 
effect of burnt lime is necessary. The relative value of the lime, the 
cost per ton, the freight and the cost of application must be con- 
sidered. For a rough calculation 50 pounds of burnt lime is con- 
sidered equal to 75 pounds of hydrate and to 100 pounds of ground 
limestone. 

Problem 1. — A farmer located on land already sufficiently fri- 
able, wishes to apply one ton of burnt lime or its equivalent in other 
forms. Burnt lime costs him $5.00 per ton f. o. b., hydrate lime 
$4.00 and ground limestone $2.25 per ton. Freight is 25j£ per ton, 
as is also hauling and application together. Which form of lime 
should the farmer buy ? 

Problem 2. — The next year the f. o. b. price of lime changed to 
$4.90, $3.00 and $2.00 for the burnt lime, the hydrate and the 
limestone, respectively. Considering freight and cost of haul and 
application the same as before, what form should be purchased ? 

Problem 3. — This same farmer can purchase marl at $1.00 per 
ton, but he must load it himself and haul it three miles over a dirt 
road. It is impure, carrying only two-thirds the calcium that the 
limestone has. From conditions in your locality how would you 
consider the desirability of purchasing this form of lime as com- 
pared with those forms mentioned in Problem 2? 



CHAPTER XV 
THE PURCHASE AND MIXING OF FERTILIZERS 

It is hardly three-quarters of a century since the fertilizer 
industry began its development. In that time the use of 
commercial fertilizers has spread to all the important agri- 
cultural states of this country. Their sale amounts to 
more than $110,000,000 annually, of which fully one-half 
is expended by the farmers of the South Atlantic states, 
in an area lying within three hundred miles of the seaboard. 
Nearly one-half of the remainder is purchased in the Middle 
Atlantic and New England states, while only about five 
percent is used west of the Mississippi river. 

A large utilization of fertilizers in a region is often, but 
not always, an indication of an intensive agriculture. The 
importance of fertilizers in farm practice and the large 
expenditure that their use involves, together with the possi- 
bilities for profit, when they are properly used, make it de- 
sirable that those who utilize fertilizers should thoroughly 
understand the commercial, as well as the agricultural, 
values of these products. 

252. Brands of fertilizers. — The various fertilizer con- 
stituents or 'carriers that have been described are purchased 
by fertilizer manufacturers, who mix them into various 
combinations, each of which is called a brand. Each of 
these brands usually contains nitrogen, phosphoric acid 
and potash, in which case it is called a complete ferti- 

196 



THE PURCHASE AND MIXING OF FERTILIZERS 197 




198 SOILS AND FERTILIZERS 

lizer, although occasionally a brand of fertilizer will have 
only two carriers. Each brand is given a trade name, fre- 
quently implying the usefulness of the fertilizer for some 
particular crop, but without reference to the character 
of the soil on which it is to be used. It is better, how- 
ever, to purchase a fertilizer on the basis of its composi- 
tion rather than because of its name. The composition 
of fertilizers for different crops will be discussed later (see 
§ 261). 

If, in compounding a fertilizer, those carriers are used 
that are difficultly soluble, the fertilizer is not so valuable 
as if composed of easily soluble substances. The solubility 
as well as the percentage of each ingredient should be known 
to the purchaser. 

253. High-grade and low-grade fertilizers. — A fertilizer is 
known on the market as high-grade or low-grade, depending 
on the percentage of fertilizing constituents that it contains, 
or on the availability of its plant-food materials. Low-grade 
fertilizers cost less than high-grade because the} r contain 
less plant-food material or because they are less soluble, 
although the price of a pound of the plant nutrients may be no 
less, and, in fact, is usually more. The low-grade product 
is encumbered with a large amount of inert material, that 
adds to the cost of transportation and handling, without 
adding to the value of the fertilizer. For these reasons the 
cost of a pound of any one of the plant nutrients is usually 
less in high-grade than in low-grade goods. A ton of low- 
grade fertilizer may contain 500 or 600 pounds more inert 
material than a high-grade fertilizer, upon which freight 
must be paid, and which must be hauled from the station 
and spread on the field. 

The following figures were obtained by tabulating one 
hundred and thirty brands of fertilizers analyzed at the 
Vermont Experiment Station. 



THE PURCHASE AND MIXING OF FERTILIZERS 199 

Table 42. — Comparative Values of Low-Grade, Medium and 
High-Grade Fertilizers 











§« 


Cost in Cents of 


« 








g 


H a 


One Pound of 


s « 








a 






jHfl 






« 


s 






a > h 


Fertilizer 


a 


S o 


88 

§5 


£ s W 
S * B 

h a 

D O 




3 








u o 

as 


Selling P 
Total Pri 

Farmers 


H 

W5 


Cost of P 
Worth of 
inJHands 
Farmer 


d 
9 

e 


o 
a 

TO 


.a 

a 

1 


o g w 

go 3 
>2Q 


High grade . 


$26.30 


$38.93 


$12.63 


$0.48 


28 


5.7 


6.3 


67.6 


Medium grade 


18.22 


30.00 


11.78 


0.65 


31 


6.3 


7.0 


60.6 


Low grade 


13.52 


27.10 


13.58 


1.00 


38 


7.6 


8.5 


50.0 



In mixing fertilizers in a factory, it is customary to incor- 
porate with the carriers of plant nutrients more or less material 
that has no influence on plant growth, but that serves to di- 
lute the mixture and to prevent it from becoming damp by 
the absorption of moisture, and also to prevent the chemical 
interaction of the constituents. This material is called a filler. 

254. Fertilizer inspection and control. — Most of the 
states have enacted legislation providing for the inspection 
and control of the sale of commercial fertilizers. Each 
brand of fertilizer, that sells for $5.00 or more a ton, must 
pay a state license fee and each bag must bear a tag stating 
the guaranteed percentage of nitrogen, phosphoric acid and 
potash that the fertilizer contains, and giving some informa- 
tion in regard to their solubility. 

There is little uniformity in the requirements of the dif- 
ferent states. In some states a very detailed statement of 
the composition of the fertilizer and the solubility of its 
constituents is required. The following information is 
called for by some of the states. 

Percentage of nitrogen in the following forms : 



200 SOILS AND FERTILIZERS 

In nitrates and ammonium salts. These are generally 
present in nitrate of soda and sulfate of ammonia. Their 
availability has already been discussed (see § 218). 

Water-soluble organic nitrogen. This is probably not 
so readily available as the two former kinds, but differs little 
from them in this respect. 

Active water-insoluble organic nitrogen. Although not 
directly available this becomes so quickly enough for the 
crop to which it is applied to obtain part of it. 

Inactive water-insoluble organic nitrogen is that part of 
the organic nitrogen that is of little value for immediate 
plant growth. 

Percentage of phosphoric acid in the following forms : 

Water-soluble phosphoric acid, which is readily available 
(see § 227). 

Reverted phosphoric acid. Not so readily available 
(see § 227). 

Available phosphoric acid. This usually consists of the 
sum of the two forms mentioned above. Sometimes when 
this term is used no distinction is made between the water- 
soluble and the reverted, but this is not so satisfactory. 

Insoluble phosphoric acid. This is slowly available, but 
in animal products, such as bone, tankage and other slaughter 
house waste, it becomes available more quickly than if present 
in rock phosphate. However, the analysis does not distin- 
guish between the organic and inorganic carriers. 

Percentage of potash in the following forms : 

Soluble in water. 

Present as chloride, 

255.. Trade values of fertilizer ingredients. — In the 
states having fertilizer inspection laws, it is customary for 
the officers in charge of the inspection to adopt each year a 
schedule of trade values for nitrogen, phosphoric acid and 
potash in each of the carriers ordinarily found in fertilizers. 



THE PURCHASE AND MIXING OF FERTILIZERS 201 

These values are based on the wholesale market reports 
for six months preceding March 1 of each year, to which is 
added about 20 percent of the price, to cover cost of handling. 



Potato Manure "A" without Potash 1916 



Nitrogen 

Equal to Ammonia 
Soluble Phosphoric Acid 
Reverted Phosphoric Acid 
Available Phosphoric Acid 
Insoluble Phosphoric Acid 
Total Phosphoric Acid 




4.11 to 4.94 percent. 

S. to 6. 

4. to 5. 

4. to S. 

8. to 10. 
1. to 2. 

9. to 12. 



MANUFACTURED BY 

X - Y- Z -. FERTILIZER COMPANY 



Fig. 30. — Tag representative of the kind often used on bags of fertilizer 
to state the percentages of their constituents. 

The following values are for the year 1914. 
Trade Values of Plant Nutrients in Raw Materials 

Value per 

Pound 

in Cents 

Nitrogen in nitrates 18.5 

Nitrogen in ammonium salts 18.5 

Organic nitrogen in dried and finely ground fish, meat and 

blood 20.0 

Organic nitrogen in finely ground bone and tankage . . 19.0 

Organic nitrogen in coarse bone and tankage . . . . 15.0 

Organic nitrogen in castor pomace and cottonseed meal . 20.0 

Phosphoric acid, water soluble 4.5 

Phosphoric acid, reverted 4.0 

Phosphoric acid in fine bone, fish and tankage .... 4.C 

Phosphoric acid in cottonseed meal and castor pomace . 4.0 

Phosphoric acid in coarse fish, bone, tankage and ashes . 3.5 
Phosphoric acid in mixed fertilizers, insoluble .... 2.0 
Potash as high-grade sulfate, in forms free from muriate, 

in ashes, etc 5.25 

Potash as muriate 4.25 

Potash as castor pomace and cottonseed meal .... 5.0 



202 SOILS AND FERTILIZERS 

These values may be used by the consumer to calculate 
the wholesale cost of a fertilizer of guaranteed composition, 
which he can then compare with the retail price asked by 
the retail dealer. He may also compare the relative values 
of brands of similar composition offered for sale by different 
manufacturers. 

256. Computation of the wholesale value of a fertilizer. — 
Suppose that we have the following statement of the analysis 
of a fertilizer. 

Per Cent 

Nitrogen in nitrate of soda 1 

Nitrogen in dried blood 2 

Phosphoric acid, water soluble 6 

Phosphoric acid, reverted 

Potash, as muriate 10 

The number of pounds of each constituent to a ton of 
fertilizer is then found by multiplying the weight of a ton 
of fertilizer by the percentage of the constituent, thus : 

Nitrogen, as nitrate .01 X 2000 = 20 pounds per ton. 

Nitrogen in dried blood .02 X 2000 = 40 pounds per ton. 

Phosphoric acid, water-soluble .06 X 2000 = 120 pounds per ton. 
Phosphoric acid, reverted .02 X 2000 = 40 pounds per ton. 

Potash, muriate .10 X 2000 = 200 pounds per ton. 

The trade values, as published by the fertilizer inspection 
officers, are then applied to the several constituents. 

Nitrogen as nitrate 20 X $.185 =$3.70 

Nitrogen in dried blood 40 X $.20 = 8.00 

Phosphoric acid, water-soluble 120 X $.045 = 5.40 
Phosphoric acid, reverted 40 X $.04 = 1.60 

Potash, muriate 200 X $.0425 = 8.50 

$27.20 

Such a fertilizer will cost the consumer more than the fig- 
ure derived in this way, because the entire cost of mixing 
and retailing must be added to it. It may serve as a basis 
for ascertaining whether it would not be more profitable 



THE PURCHASE AND MIXING OF FERTILIZERS 203 

for a group of consumers to purchase the fertilizer ingredients 
in car-load lots and do the mixing themselves. 

It must also be remembered that this is the commercial 
value and not necessarily the agricultural value, which latter 
is determined by the profits from its use, and will depend on 
many factors. 

257. Home mixing of fertilizers. — There is a large margin 
between the trade value of fertilizer ingredients and their 
retail price as sold by the dealer. The cost of the raw ma- 
terials often doubles in the process of mixing and retailing, 
with the necessary transportation. It has been demon- 
strated that the raw materials may be purchased from the 
wholesale dealer and mixed by the consumer at a consider- 
ably lower cost than if purchased mixed from the retail dealer, 
and that the results are fully as satisfactory. 

Other advantages from home mixing are that it permits 
the farmer to use exactly the proportion of the several con- 
stituents that he desires, and that it makes unnecessary 
the handling of a large amount of inert materials frequently 
contained in mixed fertilizers. It is thus possible for him 
to ascertain, by field tests, the best proportions of the various 
fertilizer constituents to use on his own land for each of the 
crops he is growing. This knowledge makes it possible to 
decrease greatly the expenditure for fertilizers. 

258. Fertilizers that should not be mixed. — Because 
fertilizers consist of chemicals, some of which react on each 
other to form compounds different from those in the original 
substances, it is unwise to mix certain of these carriers. 
The result may be to convert soluble nutrients into insoluble 
ones, or to cause the loss of some constituent in the form 
of gas. If one is to mix his own fertilizers he must know 
what materials should not be brought in contact. The fol- 
lowing are some of the common carriers that should not 
be mixed : 



204 SOILS AND FERTILIZERS 



Caustic lime f A ., , , , 

, .,, Acid phosphate 

Wooa ashes > with { ^ . . , , 

Dissolved bone 



Basic slag 

Cyanamid 
Caustic lime 
Wood ashes 
Basic slag 



with 



Sulfate of ammonia 

Slaughter house waste containing ni 

trogen 
Farm manure 



The following mixtures should be applied immediately : 

f Nitrate of soda 
Caustic lime > with < Muriate of potash 

J [ Kainit 

Acid phosphate with Nitrate of soda or ground limestone. 

Cyanamid should not be mixed with acid phosphate if 
there is more than one part of the former to ten of the latter. 

259. Calculation of a fertilizer mixture. — In deciding 
on the composition of fertilizers the best and simplest way 
is to consider them according to the percentage of each of 
the three constituents, nitrogen, phosphoric acid and potash, 
they contain. If we decide to use a 3-8-5 fertilizer, the 
next step is to calculate how many pounds of each of the 
carriers of these substances must be used for each ton of the 
complete fertilizer, and how much filler must be added. 
Suppose we have on hand the following carriers : 

Nitrate of soda containing 15 percent nitrogen 

Acid phosphate containing 14 percent available phosphoric acid 

Muriate of potash, containing 50 percent potash 

The first step is to calculate the number of pounds of 
nitrogen, of phosphoric acid and of potash in a ton of a 
3-8-5 fertilizer. To do this we merely multiply the num- 
ber of pounds in a ton by the percent of each plant-food 
material. 



THE PURCHASE AND MIXING OF FERTILIZERS 205 

2000 X .03 = 60 pounds nitrogen per ton 

2000 X .08 = 160 pounds phosphoric acid per ton 

2000 X .05 = 100 pounds potash per ton 

The next step is to calculate the number of pounds of the 
carrier required to furnish the quantity of plant-food material 
that has just been found. This is done by dividing the 
weight of the plant-food material required by the percent 
of this particular plant-food material in the carrier that is 

to be used. 

60 + .15 = 400 pounds nitrate soda 
160 -5- .14 = 1143 pounds acid phosphate 
100 + .50 = 200 pounds muriate of potash 
1743 pounds of the three carriers 

The weights of the different carriers are then added, giving 
in this case 1743 pounds needed for every ton of fertilizer. 
The remainder of the ton (2000 - 1743 = 257 pounds) 
is then made up with a filler, consisting of sand, dry earth, 
muck, peat, sawdust or something of the kind. 

260. How to mix the ingredients. — A smooth tight floor 
is needed on which each carrier is spread in turn to break 
down the lumps. It is then passed through a coarse screen. 
A weighed quantity of the filler or principal carrier is then 
spread out in uniform depth and on top of it another carrier, 
until all are represented. Then the pile is shoveled over and 
over, and finally leveled and the process repeated until the 
ingredients are thoroughly mixed. This lot of fertilizer 
is then put in sacks and the operation repeated with another 
quantity until a sufficient amount is prepared. There 
should always be two hundred pounds or more of filler in 
each ton to give a more uniform distribution of the carriers. 

QUESTIONS 

1. In what parts of the United States are fertilizers used in 
greatest quantities ? 

2. What is meant by a brand of fertilizer ? 



206 SOILS AND FERTILIZERS 

3. What is a high-grade in distinction from a low-grade f ertilizer ? 

4. Explain what is meant by a filler. 

5. What, in a general way, does a report on the inspection of a 
fertilizer show ? 

6. How are trade values of plant nutrients evaluated ? 

7. What are the advantages to be derived from the home mixing 
of fertilizers ? . 

LABORATORY EXERCISES 

Exercise I. — Fertilizer inspection and control. 

Fertilizer laws are designed to protect the honest manufacturer 
as well as the farmer. Obtain the laws of your state which have to 
do with fertilizer inspection and control. Analyze them step by 
step with this point always in mind. Decide whether or not the 
law does really regulate and protect in the way that it should. A 
study of fertilizer bags and tags could also be made with profit. 

Exercise II. — Laboratory mixture of fertilizers. 

Materials. — Sodium nitrate, dried blood, acid phosphate, 
muriate of potash, sulfate of potash, balances, dry soil as a filler. 
You must have the guaranteed composition of each carrier. 

Procedure. — Make 2000-gram lots of the following mixtures. 
Fertilizers must be dry and fine. Put through sieve if necessary. 

No. 1. — Make up 2 kilos of a 3-7-10 fertilizer, using sodium 
nitrate, acid phosphate and muriate of potash. Add filler as nec- 
essary. 

No. 2. — Make up a fertilizer as above, using dried blood, acid 
phosphate and sulfate of potash. 

Allow these mixtures to stand for some weeks and compare. 
Also compare them as to physical condition with a ready mixed 
fertilizer of a similar guarantee. 

Exercise III. — Home mixture of fertilizers. 

If possible cooperate with some farmer in the mixing of fertilizers. 
Allow the pupils to check all calculations and to aid in the actual 
mixing of the goods. The pupils should also understand the pro- 
cedure of selecting and ordering the fertilizer carriers in order that 
every step in the process may be familiar to them. The educational 
value of a study of the crop, soil, fertilizer and rotation is a strong 
point in favor of home mixing. 



CHAPTER XVI 
THE USE OF FERTILIZERS 

We have seen that a very considerable economy in the 
purchase of fertilizers may be effected through a knowledge 
of their composition. There is still further opportunity 
for both economy and profit through a study of their use. 

261. Fertilizers for different crops. — It has already been 
pointed out that there is a difference in the ability of plants of 
different kinds to extract nutriment from the soil. Some 
crops are able to draw abundant nourishment from soils 
from which others derive but little. This may be due, in 
part, to (1) a deficiency in the soil of the particular sub- 
stance most greatly needed by the crops, or (2) the inherent 
ability of one crop to make available plant-food materials, 
while another crop may possess that quality in much less 
degree. There are therefore two ultimate considerations 
in the selection of fertilizers : (1) the nature of the soil ; 
(2) the kind of crop. The second of these will be discussed 
first. 

262. Small grains. — Most of the small grains, like wheat, 
rye, oats and barley, need the principal part of their nitrogen 
early in the season, before the soil has warmed sufficiently 
to induce the germs that produce nitrates to lay up an abun- 
dant supply. Consequently the application of nitrate of 
soda, when growth begins in the spring, is very beneficial 
to these crops. Wheat in particular needs such an appli- 
cation. Since it is a "delicate feeder" it grows best after 
fallow, or a cultivated crop, and when it follows oats, as is 

207 



208 SOILS AND FERTILIZERS 

the usual custom, it needs a complete fertilizer. Rye is a 
" stronger feeder " and does not have the same need of 
fertilization. Oats and barley, when spring sown, find more 
nitrates in the soil, because they are later than winter 
wheat in starting growth, and, as they can make better use 
of the soil fertility, they do not require so much fertilizing. 

Corn is a " strong feeder/' and, while it removes a very 
large quantity of plant-food materials from the soil, it does 
not require that these be added in a soluble form. Farm 
manure and slowly acting fertilizers may well be used for the 
corn crop. The long growing period required by the corn 
plant gives it opportunity to utilize nitrogen as that sub- 
stance becomes available during the summer, when nitrate 
formation is most active. Phosphoric acid is the substance 
usually most needed by corn. 

263. Grass crops. — Meadows and pastures are greatly 
benefited by fertilizers. The grasses are less vigorous feed- 
ers than the cereals, have shorter roots, and, when left down 
for a year or more, the formation of nitrates is much curtailed. 
There is usually a more active fixation of nitrogen in grass 
land than in cultivated land, but nitrogen thus acquired 
becomes available very slowly. Different soils and different 
climatic conditions necessitate different methods of manur- 
ing for grass. The use of nitrate is almost always attended 
with much success, even when used alone, but in most situa- 
tions a complete fertilizer is profitable. 

264. Leguminous crops. — Most of the leguminous crops 
are deep-rooted and are vigorous " feeders." Their ability 
to acquire nitrogen from the air makes the use of that sub- 
stance unnecessary except in the form of nitrate, which is 
often very effective in starting a young seeding of alfalfa. 
The nitrate probably serves to carry the young crop through 
the period preceding the development of tubercles. Potash 
salts are almost always profitably used on legumes, and 



THE USE OF FERTILIZERS 209 

phosphoric acid is also likely to be effective. For such 
crops as clover and alfalfa there should always be an ample 
supply of lime, without which these crops cannot be prof- 
itably grown. 

265. Root crops. — Most of the root crops remove very 
large quantities of plant-food materials from the soil, when 
these are present in available form. Like corn they have a 
long growing season and the slowly acting fertilizers or farm 
manure are well adapted to their use. A complete fertilizer 
in rather large quantity will usually bring a response in 
yield. For sugar beets the proportion of potash should be 
high, and for table beets and carrots there should be more 
nitrogen than for the other roots. 

266. Vegetables. — In raising some kinds of vegetables, 
the object is to produce a rapid growth of leaves and stalks 
rather than fruit or seeds, and with these lands growth should 
often be made in the early spring. Therefore, for crops 
like lettuce, radishes and asparagus a soluble form of nitro- 
gen is very desirable. For crops that are raised later 
in the season a smaller proportion of nitrogen may be used, 
and for the more slowly growing kinds of vegetables the less 
soluble fertilizers may be applied. For all vegetables farm 
manure or other organic manure should be generously used, 
as it keeps the soil in a mechanical condition favorable to 
retention of moisture, which vegetables require in large 
quantities, and it also supplies needed fertility. The very 
intensive culture employed in the production of vegetables 
necessitates the use of much greater quantities of fertilizers 
and farm manure than are used for field crops, and the great 
value of the product justifies the practice. 

267. Orchards. — In manuring orchards, it is the aim 
to maintain a continuous supply of nutrients available to 
the plants, but not sufficient for stimulation, except during 
the early life of the tree, when rapid growth of wood is 



210 



SOILS AND FERTILIZERS 



desired. During the first few years after setting out, there 
should be a liberal supply of nitrogen. An acre of apple 
trees in bearing removes as much plant-food material from 
the soil in one season as does an acre of wheat. Green- 
manures may be used to advantage in orchards, as by plant- 
ing these crops in midsummer, moisture is removed from 
the soil and the wood of the trees is thereby hardened and 
thus prepared to withstand the low temperatures of winter. 
The green-manures also hold snow on the ground, if allowed 
to stand over winter, and may then be plowed under in the 
spring. 

268. Fertilizer mixtures for different crops. — On ac- 
count of the large number of factors that enter into the pro- 
cesses of crop production, it is obviously impossible to pre- 
scribe accurately the proportion and quantity of fertilizer 
carriers that should be applied. Some rough approximation 
can, however, be arrived at on the basis of the peculiarities 
of the various classes of crops that have just been enumerated. 
It must be remembered that different soil conditions may 
materially change the proportions of the fertilizer ingredi- 
ents that should be applied. The following proportions of 
nitrogen, phosphoric acid and potash for different classes 
of crops have been proposed and have been found a fairly 
useful guide in the home mixing of fertilizers. 

Table 43. — Fertilizer Formulas for Different Crops 



Chops 


Percentage 

of 

Nitrogen 


Percentage 

of Phosphoric 

Acid 


Percentage 
of 
Potash 


Legumes (young) .... 

Small grains 

Vegetables 

Grass 

Orchard 

Roots 


1 

3 
4 
5 
4 
3 


8 
8 
8 
4 

8 

8 


10 
5 

10 
4 
6 
7 



THE USE OF FERTILIZERS 211 

A fertilizer based on the first percentages would be called 
a 1-8-10 fertilizer ; one based on the second a 3-8-5 ferti- 
lizer, and so on. In making up these formulas the carriers 
to use are indicated in the previous discussion. The quan- 
tities that it is desirable to use will depend so much on 
the natural productiveness of the soil that it is not possible 
to prescribe for soils in general. On soils of about average 
productiveness, however, a certain range for each of the 
classes of crops may be suggested. 

Legumes 100 to 200 pounds per acre 

Small grains 100 to 300 pounds per acre 

Vegetables 500 to 1000 pounds per acre 

Grass 200 to 500 pounds per acre 

Orchards 200 to 600 pounds per acre 

Roots 300 to 800 pounds per acre 

269. Fertilizers for different soils. — The best way to 
ascertain what fertilizers are needed for a particular soil is 
to test it with different lands and quantities of fertilizing ma- 
terials. It will thus be possible to estimate whether the 
three substances, nitrogen, phosphoric acid and potash 
are all needed, and in about what quantities they should 
be applied. 

A practical way is to select a level and apparently uniform 
part of a field and on it lay off plats of land eight rods long 
and one rod wide, giving an area of -£$ of an acre. These 
plats should lie parallel on their long side, but should have 
a space of at least three feet between them. The arrange- 
ment is shown in Fig. 31 on the next page, which also in- 
dicates the quantity of fertilizing substance that each plat 
should receive. 

The fertilizer used in this experiment is designed for small 
grains, the mixture being 3-8-5 if the carriers contain about 
15 percent nitrogen, 14 percent phosphoric acid and 48 per- 
cent potash respectively. If a legume or grass crop is 



212 SOILS AND FERTILIZERS 

used in the test the fertilizer should be adjusted to suit the 
crop, as stated in Table 43. If grass is the most important 



No fertilizer 



Nitrate of soda 5 pounds 

Acid phosphate 15 pounds 



Nitrate of soda 5 pounds 

Muriate of potash 2\ pounds 



No fertilizer 



Acid phosphate 15 pounds 

Muriate of potash 2| pounds 



Nitrate of soda 5 pounds 

Acid phosphate 15 pounds 

Muriate of potash 2| pounds 



No fertilizer 



Nitrate of soda 2\ pounds 

Acid phosphate 1\ pounds 

Muriate of potash 1 pound 



Fig. 31 . — Plan for a fertilizer experiment with small grains. Plats of land 
8 rods long and 1 rod wide, giving an area of 55 acre in each plat. The rate 
of application to the acre would therefore be twenty times the quantities given 
in the diagram. 

crop the test should be made with special reference to it, 
and so with any other important crop. In any case a ro- 




Plate XIII. Crop Work. — The upper figure shows a plat of timothy 
the left-hand side of which has been properly fertilized. The right-hand 
side has received no fertilizer. Note the thick stand of daisies on the 
latter. 

The lower figure illustrates the method of laying off plats for tests of 
fertilizers. 



THE USE OF FERTILIZERS 213 

tation should be followed and the system of fertilization should 
be adjusted to the rotation as explained in § 271. 

In order that the kind and quantity of fertilizer shall be a con- 
trolling factor, the plats should be well drained and well tilled 
and should not be in need of lime, which may be ascertained 
by either of the tests described in §§ 145, 146. 

270. Calculation of the results. — Each test plat has, on 
one side of it, a plat that has not been fertilized. The non- 
fertilized or check plats will not all give the same yield be- 
cause the soil differs in various parts of the field. If the 
variations in yield between check plats are not greater than 
one bushel to the acre, they may be considered as being equal. 
If a greater difference exists, the yield from each check plat 
must be subtracted from the yields of the test plats beside 
it and the result may then be considered to be the increase 
due to the fertilizer application. 

If the yield is as good, or nearly as good, on a check plat 
as it is on the corresponding test plat that lacks one of the 
fertilizing constituents, it may be concluded that the use of 
that constituent would not be a profitable investment. On 
the other hand, the very beneficial substances will be indi- 
cated by the increased yields wherever they are used. Fi- 
nally the desirable quantities will be indicated by a compari- 
son of the rates of increase on the plats receiving the full 
quantity and those receiving the half quantity of complete 
fertilizer. The tests should be continued for a period of 
three to five years in order that they shall be indicative of 
the fertilizer needs of the soil, and a rotation of crops should 
be used, with an adjustment of the fertilizer treatments to 
suit the different crops. 

271. Fertilizing the rotation. — In a rotation of crops 
fertilizers need not be applied every year. For instance a 
rotation consisting of hay, two or three years, corn, oats 
and wheat would probably not receive any fertilizers on 



214 SOILS AND FERTILIZERS 

one or two of the courses. It is desirable to make the rela- 
tively heaviest applications for the crops having the greatest 
money value. If the hay crop represents the largest pos- 
sible returns, the crop should be well fertilized. Another 
reason for giving liberal applications to the hay crop is that 
the sod is thereby increased and furnishes a larger supply 
of organic matter to be plowed under (see § 204). Corn 
is the crop of greatest importance in some localities, in 
winch case it should be well fertilized. Farm manure is 
usually the best fertilizer for corn, but farm manure should 
be supplemented by phosphoric acid either in the form of 
acid phosphate, basic slag or floats. Oats will seldom give 
a profitable response to fertilizers which may be dispensed 
with for that crop, but should be applied in the fall in prep- 
aration for wheat. It is hardly necessary to say that winter 
wheat should have the nitrogen applied in the spring in the 
form of nitrate of soda, while the phosphoric acid and potash 
should be harrowed in before planting. 

272. Methods of applying fertilizers. — The distribution 
of fertilizers by means of machinery is much more satis- 
factory than is broadcasting by hand, because the former 
method gives a more uniform distribution. Cereal and 
other crops are now usually planted with a drill, or a planter 
provided with an attachment for dropping the fertilizer at 
the same time that the seed is sown, the fertilizer being, by 
this method, placed under the surface of the soil. Broad- 
casting machines are also used, which leave the fertilizer 
uniformly distributed on the surface of the ground, thus per- 
mitting it to be applied and harrowed in a sufficient time 
before the seed is planted to prevent injury to the seed 
through the chemical activity of the fertilizer. 

Corn-planters with fertilizer attachment deposit the ferti- 
lizer beneath the seed, so as not to bring the two in contact. 
Grain drills do not do this and if the quantity of fertilizer 



THE USE OF FERTILIZERS 215 

exceeds 300 or 400 pounds to the acre, it is better to apply 
it before seeding. Grass seed and other small seeds should 
be planted only after the fertilizer has been mixed with the 
soil for several days. 

273. The limiting factor. — Attention has been called to 
the important influence that any condition unfavorable to 
plant growth is sure to exercise in curtailing yield of crops. 
If poor drainage is the difficulty, crop yields may be reduced 
to almost nothing, while if this be corrected a very productive 
piece of land may result. The same principle holds true 
when there is a deficiency of any one of the fertilizing sub- 
stances. There may be present in a soil an abundant supply 
of available phosphoric acid and potash, but if nitrogen is 
deficient the crop yield is limited to the size of crop that the 
quantity of available nitrogen present will produce. Each 
of the essential plant-food materials exercises this control. 
It is, therefore, a requisite in the economical use of ferti- 
lizers to have a well-balanced mixture of plant nutrients. 
The balance must be adjusted to the needs of each partic- 
ular soil, and to each kind of crop. Of course it is impossible 
to work out any fertilizer mixture that will fit these condi- 
tions exactly. These relationships are best worked out by 
field tests with fertilizer mixtures (see § 269) . 

274. The law of diminishing returns. — A small applica- 
tion of fertilizer usually effects a greater percentage increase 
of crop than does a larger application. This is unfortu- 
nate, because it means that there is a limit to the profit- 
able use of fertilizers, for although the cost of the fertilizer 
rises in direct proportion to the quantity used, the rate of 
yield decreases after a certain point has been reached, and 
consequently the value of the product finally becomes less 
than the cost of the fertilizer. This law of diminishing 
returns may be illustrated by an experiment in which floats 
were applied in several different quantities to plats of land, 



216 



SOILS AND FERTILIZERS 



each of which plats also received an application of farm ma- 
nure at the rate of 15 tons an acre. The applications of 
floats were at the rate of 200, 400, 800 and 2400 pounds to 
the acre respectively. In the following table are stated the 
increased yields over the check plats receiving the same 
quantity of farm manure but no floats. The values of 
the crops and cost of floats are reckoned on the same basis. 

Table 44. — Increased Yields and Values of Corn Resulting 
from Application of Farm Manure and Floats 



Fertilizer Treatment per Acre 


Grain 

BU. 


Value 


Cost of 
Floats 


Difference 


15 tons of manure + 200 lbs. 

floats 

15 tons of manure + 400 lbs. 

floats 


7.0 

8.3 


$4.62 
5.48 
6.73 
8.38 


$ 0.90 

1.80 

3.60 

10.80 


$3.72 
3.68 


15 tons of manure + 800 lbs. 
floats 


10.2 


3.13 


15 tons of manure + 2400 lbs. 
floats 


12.7 


2.42 loss 









It may be seen that the increase from the use of the first 
200 pounds of floats was greater than from the additional 200 
pounds, and from the next 400 pounds the increase was at 
a still lower rate. This is best shown by a curve, which may 
be seen in the upper part of Fig. 32. 

From the direction taken by the curve it may be seen that 
finally a point will be reached when there will no longer be 
any increase from larger applications of fertilizer. Long 
before that point is reached, however, the use of the ferti- 
lizer ceases to be profitable. This may be shown by another 
diagram containing curves for the value of the grain and the 
cost of the fertilizer. (See lower diagram in Fig. 32.) 

This diagram as well as the last column of Table 44 shows 
that the difference between the value of the product and the 



THE USE OF FERTILIZERS 



217 



cost of the fertilizer decreases after the lowest application, and 
that for the very heavy application there is an actual loss. 

275. Conditions that influence the effect of fertilizers. — 
The extent to which fertilizers are utilized by crops depends 




4-00 aoo /zoo /eoo zooo 

POUMDS OF FLOATS APPLIED PER, ^7CRE 




400 800 /200 /600 2000 

POUHDS OF F r LOflT5 APPLIED RER /JC&E 
Fig. 32. — In the upper diagram the heavy line shows how the yields of 
corn were increased by graduated applications of phosphoric acid in floats. 
1 1 will be seen that the increases in yields were proportionately much greater 
for small applications than for large. 

The lower diagram illustrates the rate at which the cost of the fertilizer 
approaches and finally passes the value of the product as the size of the appli- 
cation increases. 

on the presence or absence of certain conditions. The entire 
amount of any constituent of a fertilizer is never recovered by a 
crop in any one year. This is a very important consideration 
in the manuring of land, for under conditions as they fre- 
quently exist, the use of fertilizers is wasteful and extravagant. 



218 SOILS AND FERTILIZERS 

The factors, within the control of man, that affect the 
availability of fertilizers are the following : (1) the kind of 
crops ; (2) soil moisture content ; (3) soil acidity ; (4) tilth 
of the soil ; (5) organic matter in the soil. 

An undesirable condition of any one or more of these 
factors is a very common occurrence, and yet fertilizers are 
expected to produce profitable returns, in spite of these 
adverse conditions. It must be remembered that the supply 
of nutrients is only one of the conditions that influence plant 
growth. Furthermore, an economical use of fertilizers 
requires that they merely supplement the natural supply 
of plant nutrients in the soil, and that the latter should fur- 
nish the larger part of the nutrient material used by the 
crop. Finally, most fertilizers are rendered less readily 
soluble by the absorptive properties of the soil, and the re- 
lease of these substances for plant use depends to a great 
extent on the conditions enumerated above. 

276. Response of sandy and of clay soils to fertilizers. — 
It is generally recognized that a sandy soil responds more 
promptly to the application of fertilizers than does a clay 
soil. There are probably two reasons for this : (1) Absorp- 
tion may not be so complete both on account of the particles 
being larger, and because in many sandy soils the particles 
are largely composed of quartz, which does not have the 
property of forming combinations with bases, as does clay ; 
(2) Drainage and aeration are likely to be better, as are most 
of those conditions that make plant-food materials more 
available. For these reasons, a sandy soil generally makes 
a greater response to fertilizers the first year, but shows less 
effect in subsequent years unless the treatment is repeated. 
On the other hand, less fertilizing material is lost from a clay 
soil by leaching. 

277. Cumulative need for fertilizers. — It is often re- 
marked that on land habitually fertilized there is a gradually 




A sufficient supply of moisture makes a fertilizer more effective. Note 
the greater response to fertilization in the vessels having more moisture. 



Vessel 45. Moisture 30 per cent, 

Vessel 49. Moisture 15 per cent, 

Vessel 58. Moisture 30 per cent, 

Vessel 64. Moisture 15 per cent, 

Vessel 69. Moisture 30 per cent. 

Vessel 78. Moisture 15 per cent, 



no fertilizer, 
no fertilizer, 
complete fertilizer, 
complete fertilizer, 
more fertilizer, 
more fertilizer. 















. 1 1 « » 1 . 


h 




V 






, i 


_-4WilftiilI \ 1 




_ . AU / 




! 


it 




r" 




-JB-WJ 


lid 






>ji^^r 


iiilfi will 























Plate XIV — A soil may contain too much or too little moisture. The 
best crop is in the vessel having next to the largest quantity of water. 



Vessel 20. Moisture 11 per cent. Vessel 26. 

Vessel 22. Moisture 13 per cent. Vessel 28. 

Vessel 24. Moisture 20 per cent. Vessel 32. 



Moisture 25 per cent. 
Moisture 38 per cent. 
Moisture 45 per cent. 



THE USE OF FERTILIZERS 219 

increasing need for greater quantities of fertilizers. This is 
doubtless the case in many instances, and arises from neglect 
of other factors affecting soil productiveness. As we have 
seen, certain fertilizers cause the soil to lose lime, which 
results in soil acidity. Organic matter is allowed to decrease, 
and this causes the soil to become compact and poorly aerated, 
and thus, one bad condition leads to another and crops be- 
come poorer in spite of increased applications of fertilizer. 

QUESTIONS 

1. Why are some crops able to draw abundant nourishment from 
soils on which other crops yield poorly ? 

2. How do wheat and corn differ in their need of plant-food 
materials ? 

3. Why is nitrate of soda particularly beneficial to grass ? 

4. What two fertilizer materials are generally useful on legumes ? 

5. What fertilizer material is required in large amounts by most 
root crops ? 

6. What plant nutrient is especially needed by vegetables that 
are expected to make a rapid and succulent growth ? 

7. In what ways are green-manures of use in orchards ? 

8. Plan a fertilizer test similar to that shown in Fig. 31, but 
to be used with a crop of timothy instead of small grain. 

9. To what crops in a rotation of corn, oats, wheat, and grass 
would you apply fertilizers ? 

10. Explain what is meant by the limiting factor in plant growth 
with respect to the use of fertilizers. 

11. What is meant by the law of diminishing returns ? 

12. Name five soil factors within the control of man that influ- 
ence the availability of fertilizers. 

13. Give two reasons why a sandy soil responds more promptly 
to fertilizers than does a clay soil. 

14. Explain why soils sometimes demand an increasing use of 
fertilizers to maintain their productiveness. 

LABORATORY EXERCISES 

Exercise I. — Fertilization of standard rotations. 
The fertilization of the rotation is the ultimate and final consider- 
ation of any systematic use of fertilizers. While the fertilization as 



220 SOILS AND FERTILIZERS 

to amounts and mixtures is generally different for different farms, 
the place of fertilizers in a standard rotation is more or less fixed. 

Take a number of good practical rotations and indicate where in 
the succession of crops the fertilization should occur. Also suggest 
what should be the formula of each mixture used, the fertilizer 
compounds which should be carried and the amounts that might 
be applied to a given soil. 

Exercise II. — Fertilization of home-farms. 

Encourage the pupils to bring in data regarding the fertilization 
on their home farms. Tabulate, discuss and criticize such data in 
a practical way. If any of the pupils have home project gardens, 
the fertilization of such gardens should be made a special problem 
for them. 

Exercise III. — Fertilizer practice in the community. 

A fertilizer survey of the township could be made with profit 
by the teacher, visiting each farmer and making inquiry adequate 
for the purpose in view. The pupils could aid not only in the col- 
lection of such data but also in such compilation and interpreta- 
tion as would later be necessary. 

Taking the class to visit a farmer whose system of farming and 
fertilization is a practical success is to be advocated. The 
economic use of fertilizers is attained not only by scientific knowl- 
edge, but also by good sound experience and practice. 

Exercise IV. — Fertilizer experimentation. 

The measurement in crop yield of the effects from fertilizer use is 
the only true means of gauging fertilizer needs and fertilizer prac- 
tice. Whether a certain fertilizer pays is the ultimate question. 

Lay out plans for fertilizer experimentation as suggested in the 
text with the idea of taking careful data as to crop yield from the 
various treatments used and the calculation of the net returns. 

The fertilizer needs of the soil for nitrogen, phosphoric acid, 
potash and lime may be determined by the use of the various fer- 
tilizer carriers both alone and in combination. Different ready mixed 
fertilizers may also be compared. The amount of any particular 
fertilizer that may most economically be used can be tested by vary- 
ing the applications of the same mixture. The relation of lime, farm 
manure and time of application to the effectiveness of any particur 
lar fertilizer may also be made a subject of experimentation. 



CHAPTER XVII 
FARM MANURES 

The use of animal manure to enrich the soil antedates 
written history, and it is still the most commonly and widely 
used fertilizer. It is produced on nearly every farm. Mar- 
ket-gardeners, who usually keep few animals, buy large quan- 
tities of horse manure from cities. Its use constitutes a 
way of returning to the land a part of the plant nutrients 
taken up by crops, as well as replacing some of the or- 
ganic matter destroyed by cultivation. Farm manure con- 
tains nitrogen, phosphoric acid, potash, lime and the other 
ingredients removed from soils, and hence is a direct ferti- 
lizer. In addition to these it contains a large quantity 
of organic matter, which by its influence on tilth, moisture 
and absorptive properties is a valuable soil amendment, and 
finally it favors, in a number of ways, a vigorous bacterial 
activity that does much to bring plant nutrients into an 
available condition. 

278. Solid and liquid manure. — Farm manure is made 
up of the solid excreta of animals, the urine, which is usually 
largely absorbed by the solid ingredients, and the litter 
used for bedding the animal. As these constituents differ 
greatly, not only in composition but also in physical proper- 
ties, .their proportions must appreciably affect the agri- 
cultural value of the manure. Litter usually does not have 
as high a fertilizer value as do the solid and liquid excreta. 
Of the excreta the larger part is solid and the smaller is 
urine. The ratios may be found in Table 45. The propor- 

221 



222 



SOILS AND FERTILIZERS 



tion of litter is variable, depending on the extent to which 
bedding is used. 

' 279. Chemical composition of manures. — From what 
has already been said regarding the variable nature of ma- 
nure, it will be understood how difficult it is to give a state- 
ment of the composition of a representative sample of ma- 
nure. The following table gives the results of an analysis 
that may be considered fairly representative of mixed fresh 
manure from several different classes of animals. 

Table 45. — Pounds of Water and Plant-Food Materials in 
One Ton of Solid Excreta, One Ton of Liquid Excreta 
and in One Ton of Entire Excreta of Several Different 
Classes of Animals 





Pounds in a Ton 


Percentage of Solid and Liquid Parts of 
Excrement 


Water 


Nitro- 
gen 


Phos- 
phoric 
Acid 


Potash 


f Solid, 80 percent 

Horse < Liquid, 20 percent 

[ Entire excreta 

f Solid, 70 percent 

Cow < Liquid, 30 percent ..... 
[ Entire excreta 

f Solid, 67 percent 

Sheep < Liquid, 33 percent 

[ Entire excreta 

( Solid, 60 percent 

Swine < Liquid, 40 percent . . . . . 
[ Entire excreta 


1500 
1800 
1560 

1700 
1840 
1720 

1200 
1700 
1360 

J 600 
1940 
J/40 


11 

27 
14 

8 
20 
12 

15 

27 
IP 

11 

8 
10 


6 

trace 

5 

4 

trace 

3 

10 
I 

7 

10 

2 

7 


8 
25 
11 

2 

27 
9 

9 
42 
20 

8 
9 

8 



This table shows that the solid excrement constitutes by- 
far the larger part of the total. It also shows that a ton of 
liquid excreta is generally richer in nitrogen and potash than 



FARM MANURES 



223 



is an equal quantity of solid excrement, but in the case of 
swine there is little difference between the solid and liquid 
excreta in this respect. 





JE 




S* 



f 0l 









TOTAL PHOSPHORIC POTASH 

MITR06EN ACID 

0.5% 0.5% 0.6% 

Fig. 33. — A farm manure containing 0.5 percent nitrogen, 0.3 percent 
phosphoric acid and 0.6 percent potash will, on the average, have these 
constituents divided between the solid and liquid parts of the manure in 
the proportions shown above. 

280. Farm manure an unbalanced fertilizer. — A mix- 
ture of horse and cow manure, with an ordinary quantity 
of straw litter will have a composition somewhat as follows : 



224 



SOILS AND FERTILIZERS 



Constituents 




Pounds 
Per Ton 



Water . . . 
Dry matter 
Nitrogen . . 
Phosphoric acid 
Potash . 



1460 

540 

10 

5 

12 



Assuming that one-half of the nitrogen, one-fifth of the 
phosphoric acid and one-half of the potash are readily avail- 
able, twenty tons of mixed manure would be equivalent to 
one ton of a 5-1-6 fertilizer. Comparing this with any 
ordinary fertilizer, it is evident that it is high in nitrogen 
and very low in available phosphoric acid. This suggests 
that for its most effective use farm manure should be sup- 
plemented by some form of phosphoric acid. As an illustra- 
tion of the advantage of supplementing farm manure by 
phosphoric acid see Table 52. 

281. Quantities of manure voided by animals. — An idea 
of the quantity of excreta, solid and liquid, produced by 
different animals may be obtained from the following table : 

Table 46. — ■ Excreta from Various Farm Animals to the 1000 
Pounds Live Weight 



Animal 


Pounds per 


Day 


Tons per Year 


Horse 


50 
70 
40 
85 
34 


9.1 


Cow 


12.7 


Steer 


7.3 


Swine 


15.5 


Sheep 


6.2 



282. Effect of food on composition of manure. — The 
richer the food in nitrogen and other plant-food materials, 
the more of these there will be in the manure. This has 



FARM MANURES 



225 



been demonstrated by a number of experiments, from which 
the following have been selected. 

Table 47. — ■ Effect of Food on Composition of Animal and 
Poultry Manure 





Pounds peb Ton op Manure 


Ration 


Nitrogen 


Phosphoric 
Acid 


Potash 


Fed to steers 

Corn and mixed hay 

Corn, oil meal and hay .... 

Corn, oil meal and clover 
Fed to fowls 

Nitrogenous ration 

Carbonaceous ration 


29.80 
31.00 
33.60 

16.00 
13.20 


10.53 
10.99 
11.91 

18.78 
14.65 


26.64 
24.48 
24.96 

6.48 
5.04 



283. Commercial evaluation of manures. — As a means 
of comparing manures, they may be evaluated in a manner 
similar to that used with commercial fertilizers. This, 
however, fails to place any value on the organic matter, 
which is undoubtedly of much benefit to the soil. In the 
following table are given the values of manures produced 
by different animals based, in part, on the composition given 
in Table 45 when the nitrogen is considered to be worth ten 
cents a pound, the phosphoric acid two and one-half cents 
and the potash four cents. 

Table 48. — Value of Excreta Produced by Several 
Farm Animals 



Animal 


Value per Ton 


Swine excreta 


$1.50 


Cow excreta 


1.64 


Horse excreta 


1.97 


Sheep excreta 


2.87 


Poultry excreta 




4.80 









226 



SOILS AND FERTILIZERS 



If the mixed horse and cow manure together with litter, 
similar to that referred to in section 280, be made the 
basis of the calculation, the evaluation would be $1 .60. Dilu- 
tion of the plant-food materials due to the litter tends to 
reduce the value. 

284. Agricultural evaluation of manures. — The com- 
mercial value may be quite different from the agricul- 
tural value, which is calculated from the increased crop 
production resulting from the use of the manure. This 
will vary with different soils, but even on similar soils it 
will vary with different manures. The following table gives 
the results of an experiment in which treated and untreated- 
manures were evaluated commercially and were then applied 
to the land. The value of the increased crops in a three 
years' rotation was then calculated in terms of financial 
return to the ton of manure applied : 



Table 49. 



Commercial and Agricultural Evaluation of 

Manures 



Manure 


Commercial 
Value 


Agricultural 

Value 


Yard manure untreated .... 
Yard manure plus floats .... 
Yard manure plus acid phosphate . 
Yard manure plus kainit . . . 
Yard manure plus gypsum . . . 


$1.41 
2.04 
1.65 
1.45 
1.48 


$2.15 
3.31 
3.67 
2.79 
2.76 



285. Deterioration of farm manure. — There is always a 
loss in the value of farm manure on standing. The ways 
in which this is brought about are : (1) fermentation ; (2) 
leaching. The first of these is a natural process, common 
to all farm manure on standing, and not occasioned by any 
outside agencies. The second is due to the running off of 



1 















SB 




i 



Plate XV. Manures. — Farm manure is becoming relatively more 
scarce every year. Its protection is becoming more essential to success- 
ful farming. 



FARM MANURES 227 

the liquid portion of the manure, and to the exposure of the 
manure to rain. 

286. Fermentations of manure. — The mixture of solid 
and liquid excreta together with litter used as bedding con- 
stitutes a wonderfully favorable material for the growth of 
bacteria, the number of which frequently amounts to many 
billion in a gram of manure. This is many times more 
than are found in soil. It is then small wonder that fer- 
mentations proceed at a prodigious rate in a manure heap. 
These fermentations are produced both by bacteria requiring 
oxygen for their activity and by those that need little. The 
fermentations on the outside of the heap are different from 
those on the inside, where air does not readily penetrate, 
but as fresh manure is thrown on the pile from day to day, 
most of the manure first undergoes fermentation in the pres- 
ence of air and afterwards without air. 

It is through the action of germs on the nitrogenous com- 
pounds of manure that loss of value through fermentation 
occurs. In the presence of air ammonia is formed, and this 
being in a volatile form, is likely to escape. The drier the 
heap, the more likely the ammonia is to escape. 

The fermentations in the interior of a moist manure heap 
are, in the main, favorable to the production of readily 
available plant-food material. It is desirable to keep the 
heap as compact as possible, and to prevent it from becom- 
ing dry by the application of water in amounts sufficient to 
keep the heap moderately moist without leaching it. In 
the arid and semi-arid parts of the country, this is an im- 
portant precaution to be taken in the preservation of farm 
manure. 

287. Leaching of farm manure. — When water is allowed 
to soak through a manure heap and to drain away from it, 
there is carried off in solution, and to some extent in sus- 
pension, more or less of the organic matter and plant-food 



228 



SOILS AND FERTILIZERS 



materials that are soluble in water and that consequently 
represent the most valuable part of the manure. As about 
one-half of the nitrogen and two-thirds of the potash of farm 
manure is in a soluble condition, the possibility of loss by 
leaching is very great. Even phosphoric acid may thus 
be removed. 

It is rather difficult to distinguish between the losses due 
to fermentation and those caused by leaching. In an experi- 
ment conducted in Canada a carefully mixed quantity of 
farm manure was divided into two parts, one of which was 
placed in a bin under a shed, the other was exposed to the 
weather outside, in a similar bin. After *a year the two por- 
tions were analyzed and the losses thus computed are stated 
in the following table. 

Table 50. — Losses by Fermentation Alone and by Fermen- 
tation and Leaching Combined 



Constituent Lost 



Percentage Loss 




Organic matter 
Nitrogen . . 
Phosphoric acid 
Potash . 



288. Protected manure more effective. — Over a period 
of fourteen years, in a three year rotation of corn, wheat 
and hay at the Ohio Experiment Station, stall manure gave 
an average yield of 30 percent more than did equal quantities 
of yard manure. This gives a fair basis on which to cal- 
culate whether it would pay to protect the manure when the 
expense of doing so, and the quantity of manure produced, 
are considered. 



FARM MANURES 



229 



289. Reinforcing manure. — Various substances are in- 
corporated with animal manures, either in the stall or in 
the heap, for the purposes of : (1) curtailing loss by leaching 
and fermentation, and (2) balancing the manure in order to 
better adapt it to the needs of most crops. The latter has 
been mentioned in section 280. The materials commonly 
used for these purposes are gypsum, kainit, acid phosphate 
and floats. 

Experiments at the Ohio Experiment Station indicate that 
the conserving effect is slight, but that the benefit due to 
reinforcing is considerable when acid phosphate or floats 
are used. To ascertain the conserving properties of several- 
substances, each was mixed with the manure at the rate of 
40 pounds to the ton, and the loss of fertilizing value was 
computed from analyses after the mixtures had stood from 
January to April. The results are shown in the following 
table : 



Table 51. 



Effect of Reinforcing Materials on Conserva- 
tion of Fertility in Farm Manure 



Materials Used 


Value of Ton of Manure 


Percentage 


In January 


In April 


Loss 


None 

Gypsum 

Kainit 

Floats . • 

Acid phosphate 


$2.19 
2.05 
2.24 
2.81 
2.34 


$1.41 
1.48 
1.45 
2.04 
1.65 


36 
38 
35 
24 
29 



The actual agricultural value of the reinforced manure was 
ascertained from tests covering a period of fourteen years 
in a rotation of corn, wheat and hay, of which the results 
were as follows : 



230 SOILS AND FERTILIZERS 

Table 52. — Financial Results op Reinforcing Farm Manure 



Value of Net In- 
creased Yield to 
the Ton of Manure 



Manure alone .... 
Manure plus gypsum . . 
Manure plus kainit . . . 
Manure plus floats . . . 
Manure plus acid phosphate 



$3.31 
3.56 
3.71 
4.49 

4.82 



It has already been remarked that farm manure is deficient 
• in available phosphoric acid, and this experiment demon- 
strates the benefit to be gained by reinforcing it with a phos- 
phoric acid fertilizer. 

290. Methods of handling manure. — The least oppor- 
tunity for deterioration of farm manure occurs when it is 
hauled directly to the field from the stall and spread at once. 
Manure may even be spread on frozen ground or on snow, 
provided the land is fairly level and the snow is not too deep. 
However, it is not always possible to follow this method and 
manure must sometimes be stored. In the storage of ma- 
nure the two important conditions are a sufficient but not 
an excessive supply of moisture, and a well-compacted mass. 
Water draining away from a manure heap, and a fermenta- 
tion producing a white appearance of the manure under the 
surface of the pile (" fire fanging "), are both sure indications 
of unnecessary loss in its fertilizing value. 

291. Covered barnyard. — The best method of storing 
manure is in a covered yard in which the cattle are allowed to 
exercise and thus to trample and compact the mixed manure 
from the barn. The advantage to be gained from the tram- 
pling is brought out by some Pennsylvania experiments in 
which the losses of fertilizing constituents were compared 
when the covered manure was trampled and when it was not. 



FARM MANURES 



231 



Table 53. — Loss of Fertilizing Constituents from Farm 
Manure in Covered Sheds when Trampled and when 
Not Trampled 





Percentage Loss op 


Treatment of Manttre 


Nitrogen 


Phosphoric 
Acid 


Potash 


Covered and trampled 

Covered and not trampled .... 


5.7 
34.1 


5.5 
19.8 


8.5 
14.2 



292. Application of manure to land. — In applying farm 
manure to the field, it is customary either to throw it from 
the wagon in small heaps, from which it is distributed later, 
or to scatter it as evenly as possible immediately on hauling 
it to the field. The use of the automatic manure-spreader 
accomplishes the latter procedure in an admirable manner. 
As between these two methods, the advantage, so far as the 
conservation of fertility is concerned, is with the practice of 
spreading immediately. When piled in small heaps, fer- 
mentation goes on under conditions that cannot be controlled, 
and that may be very unfavorable. The heaps may dry 
out, and thus lose much of their nitrogen, or they are likely 
to leave the field not uniformly fertilized because of the 
leaching of some of the constituents of the manure into the 
soil directly under and adjacent to the heap. On the other 
hand, when spread immediately, little fermentation takes 
place, as the manure does not heat, and the soluble sub- 
stances are leached quite uniformly into the soil. Plowing 
should follow as closely as possible the spreading of the 
manure, except when it is intended for a top dressing. 

293. Place of farm manure in crop rotation. — When a 
crop rotation includes grass or clover as one of the courses, 
the application of farm manure may well be made at that 
time as a dressing. It can thus be spread at times when 
cultivated land would not be accessible, and the crop of hay 



232 



SOILS AND FERTILIZERS 



will profit greatly. Sod, when plowed under, is frequently 
planted to corn — a crop that is rarely injured by farm ma- 
nure. Experiments in Illinois indicate the great response 
of clover to farm manure, as compared with oats and corn. 



Table 54. — Increased Crop Yields and Values When Manure 
Was Applied to Corn and Oats and to Clover 





Percentage Increase 
in Yield 


Percentage Value 
of Increase 


Treatment 


Corn and 
Oats 


Clover 


Corn and 
Oats 


Clover 


Manure 

Manure, lime and phosphate 


11 

30 


92 
141 


$ 7.53 
12.21 


$10.08 
15.48 



QUESTIONS 

1. What plant nutrients does farm manure contain, and what 
indirect fertilizing material ? 

2. In what ways is the organic matter of farm manure beneficial 
to soils ? 

3. Which is richer in plant-food materials, liquid or solid 
manure ? 

4. What constituent should farm manure have added to it in 
order that it should be a well-balanced fertilizer ? 

5. What farm animal produces the largest quantity of manure 
for every 1000 pounds of live weight ? 

6. Which produces the more valuable manure, a ration rich 
in plant-food materials, or one poor in these substances ? 

7. Which of the farm animals furnishes a manure having the 
greatest commercial value a ton ? 

8. In what two ways does farm manure suffer loss on standing ? 

9. How is nitrogen likely to be lost by fermentation, and what 
condition is likely to bring this about ? 

10. What substances are lost by the leaching of manure ? 

11. What materials are used for conserving manure ? 

12. Is it better to store manure, or to haul it directly to the land ? 
Why? 

13. Discuss the place of manure in the crop rotation. 



FARM MANURES 233 



LABORATORY EXERCISES 

Exercise I. — Study of farm manure. 

In one or more trips through the community the class may study 
in a practical way the following points regarding farm manure and 
its utilization. 

1. Enter a horse stable where fresh manure is lying in the stalls. 
Observe the odor of ammonia. Explain the reason for such an odor 
and its significance. 

2. Compare horse manure and cattle manure as to weight, struc- 
tural condition and amount of water. What relation may these 
characteristics have to fermentation and to the handling of the 
manures ? 

3. In the same way compare swine, sheep and poultry manures. 

4. Examine the teachings from an exposed manure pile. What 
is the color of such liquid and what plant-food materials does it prob- 
ably contain ? 

5. Study the various ways of handling manure that are in vogue 
in the community. List and discuss their good and poor points, 
remembering that the method that would entail the least loss of 
plant-food material may not always be practicable, due to lack of 
capital or to the press of the season's work. The common ways 
of handling manure are : hauling directly to the field and either 
(1) spreading or (2) leaving in piles for later distribution, (3) stor- 
ing in a covered barnyard, (4) storing in a manure pit, (5) allowing 
manure to be tramped down behind the animals or (6) storing in 
piles either under cover or exposed. 

6. Study the mechanism and operation of a manure-spreader. 
An efficient spreader should run easily and yet distribute the manure 
evenly and in a finely divided condition. 

Exercise II. — Experiments with farm manure. 

Plat experiments similar to those suggested in Exercise IV, Chap- 
ter XVI might be carried out with profit with farm manure. The 
effect of different amounts of manure, the relative returns of manure 
from different classes of animals, the influence of lime on the return 
from the application of manure, and the residual influence of manure 
are only a few of the possible tests that might be made. 

Tests as described in Exercise III, Chapter XI might be carried 
out with manure as well as with commercial fertilizers and lime if 
plats of soil are not available. 



234 SOILS AND FERTILIZERS 

Exercise III. — The value of manure on the home-farm. 

From the data in the text, have each student calculate the 
probable quantity of manure produced on his home-farm. Have 
him calculate the commercial value of this manure. Then from the 
way in which the manure is handled have him estimate the loss 
which occurs to this manure. Now discuss the probable agricultural 
value of the manure as compared with its original commercial value. 

Exercise IV. — Reinforcement of farm manure. 

In cooperation with some near-by farmer, reinforce some farm 
manure, allowing the pupils to aid not only in the actual work, but 
in the determination of the kind and amount of reinforcing materials 
to use. Calculate from the quantities used and their composition 
as given in the text, the probable composition of the manure after 
the treatment and determine whether it has become a properly 
balanced material. The reinforced manure should be spread in 
the field so that its influence on the succeeding crop may be com- 
pared with untreated manure. Reinforcements with different ma- 
terials may even be compared under actual field conditions. 

Exercise V. — Building of a compost pile. 

Farm manure in a compost pile supplies the organisms which 
bring about the decay of the sod, leaves or other plant materials 
which are. to be reduced to simple compounds. Composted mate- 
rials are of especial value in greenhouses and gardens in supplying 
organic matter to the soil, that a good structure may be maintained. 

Choose a level spot on which to locate the compost pile. First 
put down a layer of sod, moistening if necessary until optimum con- 
ditions are attained. Next apply a thin layer of fine, well-rotted 
manure, then sod and so on till the pile is complete. The pile may 
be as large as necessary or convenient and should be level on top to 
prevent the rainfall from running off the surface. If the interior of 
the pile is moist to begin with, it will stay moist through the period 
given to fermentation. Six months or a year are necessary for 
effective composting. 

Other materials than sod may be placed in a compost heap, 
such as leaves, vines of all kinds, rotted vegetables, garbage, small 
sticks, etc. It is a good practice also to add lime to the pile to keep 
it sweet. If the material is to be used as a fertilizer as well as to 
condition the soil, acid phosphate may also be added. 



CHAPTER XVIII 
GREEN-MANURES 

Crops that are grown primarily for the purpose of being 
plowed under to improve the soil are called green-manures. 
They may benefit the soil in one or more of four ways : (1) By 
utilizing soluble plant-food material that would otherwise 
leach from the soil ; (2) by incorporating vegetable matter 
with the soil ; (3) leguminous crops, when used, add to the 
available nitrogen of the soil ; (4) plant-food materials from 
the lower soil may be brought to the surface soil. 

A large number of crops may be used for this purpose, 
while the climate determines to some extent which crops 
should be used. Crops that, can be planted in the fall to 
grow during the cool weather may be utilized when otherwise 
the land would frequently lie bare. Leguminous crops have 
the great advantage of acquiring nitrogen from the air. Deep- 
rooted crops usually accumulate a large amount of nutriment 
from the soil and considerable from the lower depths. They 
are therefore useful in bringing plant-food material to the 
upper layers of soil. Succulent crops decompose easily, and 
dry out the soil less, when plowed under, than do woody crops. 
Crops with extensive root- systems prevent loss of soluble 
matter more thoroughly than do plants with small root 
systems. 

294. Protective action of green-manures. — It has been 
shown in section 121 that the growth of crops on land may 
prevent a large loss of plant-food material, especially nitrogen 

235 



236 



SOILS AND FERTILIZERS 



and lime, in drainage water. If, therefore, green-manure crops 
cover the soil, when otherwise nothing would be growing on it, 
they exercise a protective action. In the case of orchards a 
green-manure crop saves much nutriment as compared with 
clean cultivation. A catch-crop, like rye, that is sown in the 
fall after a summer crop has been harvested and is plowed 
under in the spring, saves some plant-food material. 

295. Materials supplied by green-manures. — Probably 
the most beneficial effect exerted by green-manures is the ad- 
dition of organic matter to soil. Practically the only source 
of organic matter is in the form of farm manure or of plant 
residues. Farm manure is yearly becoming more scarce 
and expensive. Some substitute must be found. In an 
average crop of green-manure, from five to ten tons of 
material is turned under. Of this, from one to two tons is 
dry matter, and from four to eight tons is water. This would 
correspond to a dressing of four to eight tons of farm manure, 
so far as the organic matter alone is concerned. 

Legumes add nitrogen as well as organic matter. The 
nitrogen contained in a ton of the green crop, when in a con- 
dition to plow under, is as follows : 



Table 55. 



Quantities of Nitrogen in Some Leguminous 
Green-Manure Crops 



Crop 



Red or mammoth clover 
Crimson clover . 
Alsike clover .... 

Alfalfa 

Cowpeas 

Soy beans 

Canada field peas . 



Nitrogen 
per Ton, 
Pounds 



10 
9 
10 
14 
8 
10 
11 



Probable 
Yield per 
Acre, Tons 



Nitrogen 

per Acre, 

Pounds 



60 
54 
50 
112 
48 
60 
55 



GREEN-MANURES 



237 



Not all of the nitrogen contained in these crops is taken 
from the air. On soils rich in nitrogen, a considerable pro- 
portion may be obtained from the soil. On poor soils, the 
proportion derived from the atmosphere is considerably 
larger. Soils needing nitrogen most are those that benefit 
most largely from its application. 

296. Transfer of plant-food materials. — There is a trans- 
fer of plant nutrients in a double sense : (1) removal of these 



L055 LAR6ELY ORGANIC * 
WITH SOME NITR06EN 
AND PHOSPHORIC ACID 



ANIMAL 



TO MARKET 



LAR6E L055 OF ORGANIC ^ 
MATTER, NITROGEN, PHOS- 
PHORIC ACID AND POTASH 




GREEN MANURE 



Fig. 34. — Movements of plant-food materials. After absorption by the 
plant they may be returned in whole or in part to the soil. If grain and 
straw or hay are sold nothing but the stubble and roots are returned. If 
fed to animals, part may be returned in the manure. If plowed under as 
green-manure, all are returned. 

substances from combination with other minerals and their 
conversion into combinations with organic matter; (2) re- 
moval from lower soil by absorption by roots and the deposi- 
tion of this material in the upper layer of soil when the plant 
dies and is plowed under. The first of these transfers results 
in an improved condition of the plant nutrients, because in 
the combinations with organic matter they are in general 
more available to plants than when in combinations with 



238 



SOILS AND FERTILIZERS 



inorganic matter. By the second form of transfer the nutri- 
ents in this available form are deposited in the upper soil from 
which most crops draw the larger part of their nutriment. 

297. Crops used for green-manuring. — The following table 
contains a list of the plants commonly used as green-manures 
both in cultivated fields and in orchards, together with some 
information as to the season of the year when they may be 
used and whether adapted to northern or southern conditions. 

Table 56. Crops Used as Green-Manures 



Legumes (annual) 

Canada field pea 

Hairy vetch 

Crimson clover 

Peanut 

Velvet bean 

Soy bean 

Cowpeas 

Legumes (biennial or perennial) 
Red or mammoth clover . . . 

Alsike clover 

Alfalfa 

Sweet clover 

Non-Legumes 

Rye 

Oats 

Buckwheat 

Cowhorn turnips 

Mustard 

Rape 



Season 



summer 

winter 

winter 

summer 

summer 

summer 

summer 

one year at least 
one year at least 
one year at least 
one year at least 

winter 

fall or early spring 

fall and summer 

summer 

summer 

summer and fall 



Region 



Northern states 
Northern and southern states 
Middle and southern states 
Middle arftl southern states 
Middle and southern states 
Middle and southern states 
Southern states 



Northern 

Northern states 

Northern and southern states 

Northern and southern states 



Northern and middle states 
Northern and middle states 
Northern states 
Northern states 
Northern states 
Northern states 



A soil that has become less productive under cultivation, 
and that must be improved before profitable crops can be 
grown, receives more benefit from the use of legumes than 
from any other crop. The legume to use is naturally the one 
best adapted to the region in which the soil is located. 

The perennial or biennial legumes are too slow of growth 
really to be considered green-manure crops. They are like 



• to"* 



* - 

i %X4> ... 








Plate XVI. Soil Covers. — Cover-crops may consist merely of 
weeds allowed to grow voluntarily, as shown in the upper figure, or of 
grain or other planted crops, as shown in the lower. 



GREEN-MANURES 239 

timothy and other grasses and can well be grown for hay, only 
the sod being plowed under. Only in the case of very much 
run down soils are these crops plowed under. Crimson 
clover is an annual, and in the central and southern states 
may be sown in the fall and plowed under in the late spring, 
thus making use of a period of the year when the ground is 
least likely to be occupied by a crop. Cowpeas, soy beans 
and field peas must be raised during the summer months. 
Vetch promises to be a satisfactory green-manure for winter 
use in the northern states, when the cost of seed becomes 
less than 'it is at present. 

Where it is desired to keep a crop on the soil during the 
autumn, winter and spring, for the purpose of utilizing the 
soluble plant-food material, the cereals, especially rye, are 
useful. Buckwheat, on account of its ability to grow on poor 
soil, is adapted to use as a green-manure, but it must be 
grown in the summer or early fall. 

298. When green-manures may be used. — The most 
economical way to use green-manures is between the regular 
crops, rather than to lose a crop for the purpose of applying 
green-manure. Between a small grain crop and a spring- 
planted crop, there is usually opportunity for some green- 
manure to be raised, even in the northern states. This crop 
may be rye, vetch, buckwheat or rape and in the southern 
states may be added crimson clover, which is perhaps best 
for that region. In the South, however, there is much 
more opportunity for the use of green-manure crops on ac- 
count of the longer season. Where timothy and red clover 
grow successfully, it is probably best to rely on the sod of 
these crops to furnish green-manure rather than to attempt 
any system that would necessitate dropping a crop from the 
rotation. By a judicious fertilization of the hay crops, a 
heavy sod may be produced, thus utilizing the inorganic 
matter of the fertilizer to produce organic matter in the sod. 



240 SOILS AND FERTILIZERS 

It is probably where special crops are produced that green- 
manures will reach their greatest usefulness. Their use in 
orchards is well established. For this purpose they are 
plowed under in the spring and planted in midsummer. 
Potato-growers and even market-gardeners are using green- 
manures in increasing quantity. 

299. Handling green-manure crops. — The stage of growth 
at which green-manures should be plowed under has a rather 
important bearing on their effect on the soil. In order that 
they shall decompose readily, they should be succulent when 
incorporated with the soil. If plants that have fully ripened 
are plowed under, they decompose very slowly and interfere 
with the formation of nitrates. An acid soil is unfavorable 
to the decomposition of green-manures and to the formation 
of nitrates ; hence it is desirable that lime be applied before 
planting the manure crops unless the soil is already well 
supplied with lime. 

QUESTIONS 

1. Describe what is meant by green-manure crops. 

2. State four ways in which they may be beneficial to the soil. 

3. What two substances are prevented from being leached from 
soil in large quantities by the growth of green-manure crops ? 

4. How do legumes differ from other green-manures in con- 
tributing to soil fertility ? 

5. In what two ways is there a transfer of plant nutrients brought 
about by the use of green-manures, and how do they benefit the soil ? 

6. Name five leguminous green-manure crops and state the time 
of year in which they are generally planted in your locality. 

7. Give the same information regarding five non-legumes. 

8. What is the disadvantage of plowing under green-manure 
crops when they are fully ripe ? 

LABORATORY EXERCISES 

Exercise I. — Study of green-manure in the field. 
Plan a field trip to some farm where a crop is being turned under 
for green-manure. Determine whether the time is most favorable 



GREEN-MANURES 241 

for the operation. Study the action of the plow which is being 
used and see if the depth of the plowing, the inclination of the 
furrow slice, and the covering of the green material is as it 
should be. 

Calculate the weight of the crop being turned under and with 
this as a basis, figure the pounds of water, dry matter, nitrogen, 
phosphoric acid and potash being placed in the soil per acre. If 
the crop is a legume, make a guess as to the probable gain of the soil 
in nitrogen. Is this nitrogen available or unavailable ? 

Exercise II. — Green-manure and the rotation. 

Take a number of good practical rotations ancl indicate where, 
in the succession of crops, a green-manure might be introduced. 
Encourage the pupils to bring data from their home farms for this 
study. Tabulate such material and study it in the class room. 
Also bring up the question in relation to gardening and trucking. 
Discuss the necessity, advisability and ways of introducing a green- 
manure under such conditions. 



CHAPTER XIX 
CROP ROTATION 

Early in the development of agriculture, it was understood 
that a succession of different crops on any piece of land 
gave better returns than did one crop raised continuously. 
The practice of changing the crops raised each year thus 
became customary, and the prevalence of the method among 
European peoples shows that its benefits are widely appre- 
ciated. In Great Britain and some of the countries of 
Europe, crop rotations have been most systematically 
and effectively developed. Such development has been stim- 
ulated by the diminishing productiveness of the soil, con- 
sequent upon long-continued cultivation, coupled with an 
increasing and progressive population. Regions having 
undepleted and uninfested soil, as was formerly the case in 
the prairie region of the United States, and countries that 
have an unprogressive people, like those of India, have done 
little with crop rotation. 

Another condition that discourages the use of crop rotation 
is the suitability of a region to the production of some one 
crop of outstanding value, combined, perhaps, with a rela- 
tively cheap supply of fertilizing material. These conditions 
obtain in the cotton belt of the United States. The abun- 
dant use of fertilizers may postpone for a long time the 
recourse to crop rotation. 

300. Crop rotation and soil productiveness. — There 
are many benefits to be derived from a proper rotation of 

242 



CROP ROTATION 243 

crops that are not directly concerned with soil productive- 
ness, and of these this book does not treat. In a number 
of ways crop rotation may directly affect the soil, and these 
will be discussed under several different heads. 

301. Root systems of different crops. — Some crops have 
roots that penetrate deeply into the subsoil, while others are 
only moderately deep-rooted and still others very shallow- 
rooted. Among the deeply rooted plants are alfalfa, clover, 
certain of the root crops and some of the native prairie 
grasses. Among those having moderately long roots are 
oats, corn, wheat, meadow fescue and a few other grasses, 
and among those having shallow roots are barley, turnips 
and many of the cultivated grasses. 

As plants draw their nourishment from those portions of the 
soil into which their roots penetrate, the deeper soil is not 
called upon to provide food material for the shallow-rooted 
crops, and the deep-rooted crops remove relatively less of 
their nutrients from the surface soil. It, therefore, happens 
that a rotation involving the growth of deep and shallow- 
rooted plants effects, by utilizing a larger area of the soil, 
a more economical utilization of plant nutrients than would 
a continuous growth of either kind. 

302. Nutrients removed from soil by different crops. — 
Some crops require large amounts of one fertilizing constit- 
uent, while others take up more of another. For instance, 
wheat crops are able to utilize the potassium and phosphorus 
of the soil to a considerable degree, but have less ability to 
secure nitrogen. They are usually much benefited by the 
application of a nitrate fertilizer and leave in the soil a con- 
siderable residue of nitrogen that may be available to other 
plants. A number of other crops, as, for example, beets and 
carrots, can utilize this residual nitrogen. 

Grasses remove comparatively little phosphoric acid. 
Potatoes remove very large quantities of potash. A rota- 



244 SOILS AND FERTILIZERS 

tion of crops is, therefore, less likely to cause a deficiency 
of some one constituent than is a continuous growth of 
one crop, and it utilizes more completely the available 
nutrients. 

303. Some crops or crop treatments prepare nutriment 
for other crops. — It is quite evident that leguminous crops 
not only leave in the soil an accumulation of organic nitrogen 
transformed by bacteria from atmospheric nitrogen, but that 
they leave part of the nitrogen in a form readily available 
for use by other plants. The presence of a grass crop on the 
land for several years favors the action of non-symbiotic 
nitrogen-fixing bacteria. The grass crops also leave a very 
considerable amount of organic matter in the soil, which 
by its gradual decomposition contributes both directly and 
indirectly to the supply of available nutrients. 

Stirring the soil at intervals during the summer greatly 
facilitates decomposition, and leaves a supply of easily avail- 
able food material. The introduction of intertilled crops in 
the rotation thus serves to prepare nutriment for those that 
receive no intertillage. 

304. Crops differ in their effect on soil structure. — Plants 
must be included among the factors that affect the arrangement 
of soil particles. The result of root growth is usually to im- 
prove the physical condition of soil. In general, crops with 
rather shallow and very fibrous roots are most beneficial, at 
least to the surface soil. Millet, buckwheat, barley and to a 
less extent, wheat leave the soil in a friable condition. It is on 
heavy soils that this property is most beneficially exercised. 
Tap-rooted plants, and others with few surface roots, do not 
exhibit this action. Alfalfa and some root crops are likely 
to leave the soil rather compact as compared with the crops 
mentioned above. The effect of sod is nearly always bene- 
ficial to heavy soils, and this is one of the reasons for using 
a grass crop in a rotation. 



CROP ROTATION 245 

305. Certain crops check certain weeds. — By rotating 
crops the weeds that flourish during the presence of one crop 
on the land may be greatly checked by succeeding crops. 
Some weeds are best destroyed by smothering, for which 
purpose small grain, and notably corn or sorghum grown for 
fodder are effective. Other weeds are most injured by til- 
lage, to accomplish which the hoed crops are needed ; while 
others can best be checked by the presence of a thick sod on 
the ground for a number of years. In the warfare against 
weeds that must be waged wherever crops are raised, the use 
of different crops involving different methods of soil treat- 
ment is of great service. 

306. Plant diseases and insects. — Many plant diseases 
and many insects spend their resting stages and larval exist- 
ence in the soil. A continuous growth of any one crop on the 
soil favors the increase of these species by providing each 
year the particular plant on which they thrive. A change of 
crops, by removing the host plants, causes the disappearance 
of many diseases and insects through their inability to reach 
their host plants. A long rotation, such as is frequently 
used in Great Britain, is particularly effective in eradicating 
those diseases that persist in the soil for a number of years. 

In the case of diseases that affect more than one species 
of plant, as does the beet and potato scab, there is need for 
special care in arranging the rotation. Such considerations 
may make it desirable to change the plan of a rotation. 
Another feature of the relation of crop-rotation to plant dis- 
eases is that the more thrifty growth obtainable under rota- 
tion assists the crop to withstand many diseases. 

307. Loss of plant-food material between plantings. — Many 
systems of crop rotation permit a more constant use of the 
land than is possible with continuous growth of most annual 
crops. As a soil bearing no crop on it always loses more 
plant-food material in the drainage water than does one on 



246 SOILS AND FERTILIZERS 

which plants grow, it is thus possible, by a well-chosen 
rotation, to save plant-food material that would otherwise 
be lost. 

308. Production of toxic substances from plants. — That 
soil sometimes contains organic substances that exert an 
injurious effect on the growth of certain plants is indicated by 
recent experiments and was surmised by some early writers 
on the subject. De Candolle was probably the first to ad- 
vance the idea in 1832. He suggested that at least some 
plants excrete from their roots substances that are injurious 
to the growth of the plants themselves and others of their 
species, although the excreta may be harmless or even bene- 
ficial to other plants. This he considered one of the reasons 
for the failure of many crops to succeed when grown contin- 
uously, while the same soil may be productive under a rota- 
tion of crops. 

Of recent years this subject has been investigated exten- 
sively in the United States and to some extent in Europe. 
There appears to be no doubt that toxic substances of an 
organic nature sometimes occur in soils, and there is evi- 
dence that some of them are connected with the growth of 
certain crops to which they are injurious. In most soils 
containing toxic substances the injurious effect is exerted on a 
large number of plants rather than only on those that have 
been previously grown. It is still a question to what extent 
excretion from roots or partial decomposition of plant residues 
are responsible for the poor growth that results from the 
continuous growth of crops on the same soil. 

309. Management of a crop rotation. — The advantages 
of a crop rotation are so apparent and are connected so closely 
with the profits to be derived from farming that there can be 
no doubt regarding the advisability of practicing a rotation, 
even when some one crop may be much more profitable than 
any others that can be grown. Thus even in regions and on 



CROP ROTATION 247 

soil particularly favorable to the production of any one crop, 
like tobacco, cotton, hay, corn or wheat, it will seldom be ad- 
visable to raise one crop to the exclusion of others, but the 
most rational practice will generally provide for some system 
of crop rotation. i 

There are three classes of crops that should, so far as possi- 
ble, have a place in any rotation. These are legumes, sod 
crops or grasses and intertilled crops. The value of legumes 
as nitrogen gatherers has already been discussed. It is partic- 
ularly on poor land that legumes are of most benefit, and if 
some of the tops, as for instance, the second growth of clover, 
be plowed under, their value will be greater. 

Sod crops are of great value in furnishing organic matter 
to the soil. The larger the hay crop, the more sod produced, 
which is a double incentive to the use of fertilizers and 
farm manure on this crop (see § 204). Sod also forms 
a favorable condition for the fixation of nitrogen. Legumes 
appear to have one advantage over sod crops as nitrogen 
gatherers, in that the nitrogenous matter remaining in the soil 
is more available to some crops, at least, and is more readily 
converted into nitrates. 

In each course of a rotation there should be, if possible, one 
intertilled crop, like corn, cotton, potatoes or cabbage. The 
intertilled crop should follow the sod crop, or the legume, 
because the cultivation given the soil throughout the summer 
produces a condition favorable to the decomposition of the 
organic matter furnished by the sod. Except where the con- 
servation of moisture is an important factor, the use of an 
intertilled crop is preferable to a clean fallow, as it is more 
economical of the nitrogen and lime supply, and appears to 
result in better crops the year following. 

Other crops to be used in the rotation will be determined by 
the climate, soil, market and convenience in handling. 

Fertilization of the rotation is discussed in section 271. 



248 SOILS AND FERTILIZERS 

QUESTIONS 

1. What advantage is gained by alternating deep-rooted with 
shallow-rooted plants in a rotation ? 

2. Why is a rotation of crops less likely to cause a deficiency in 
some one constituent of the soil than isi the continuous growth of 
one crop ? 

3. In what ways do some crops and some crop treatments pre- 
pare available nutriment for other crops ? 

4. How may soil structure be affected by crop rotation ? 

5. Explain the relation of crop rotation to weeds. 

6. Explain the relation of crop rotation to plant diseases and 
insects. 

7. How may plant nutrients be prevented from leaching by the 
use of the proper rotation ? 

8. What three classes of crops should have a place in any rota- 
tion and why ? 

LABORATORY EXERCISES 

Exercise I. — Crop rotations. 

Study standard crop rotations from different parts of the United 
States as to crops grown, climate, markets, fertility of the soil, 
fertilization, etc. Try to find the reason for the use of each rotation 
under its particular conditions. 

With the aid of the pupils, obtain a number of the rotations used 
in the community or county. Study these from all standpoints, 
and, if possible, suggest improvements. A rotation survey of the 
community might be made in order that data valuable to the 
farmers, as well as to the pupils, shall be obtained. The students 
should aid in this as well as in the tabulation and interpretation of 
the data. 

Exercise II. — Fertilizing the rotation. 

Under given conditions have the pupil work out the fertilization 
of a standard rotation for the locality. This means not only the 
kinds and quantities of fertilizer to apply, at what point in the 
rotation to add them and at what time of year to put on the soil, 
but also the use of lime, green manure and farm manure. Such a 
study should be a summation of many of the practices and principles 
of good soil management. 



INDEX 



Absolute specific gravity, of soil Air of soil, oxygen in, 146. 



particles, 35. 

and "heavy" soil, 35. 

and "light" soil, 35. 
Absorbed fertilizers, 100. 
Absorption, of lime by soils, 188. 

of gases, test for, 111. 

selective, 99. 

selective, test for, 111. 
Absorptive power of different crops, 

107. 
Absorptive properties of soils, 99. 
Acid phosphate, absorption by soil, 
173. 

manufacture and composition, 172. 

vs. rock phosphate, 174. 
Acid soils, described, 112. 

causes of, 113. 

crops adapted to, 116. 

crops injured by, 116. 

effect of drainage on, 113. 

effect of fertilizers on, 1 14. 

effect of green manures on, 115. 

effect of plant growth on, 114. 

litmus paper test for, 117. 

relation to bacteria, 129. 

tests for, 122, 123. 

Truogtest, 118. 

weeds that flourish on, 115. 
Adobe, composition of, 27. 

distribution of, 27. 
iEolian soils, described, 26. 

adobe, 27. 

loess, 27. 
Air of soil, composition, 145. 

control of movement, 148. 

control of volume, 148. 

demonstration of movement, 152. 

in relation to drainage, 79. 

movements, 144. 

nitrogen in, 147. 



quantities present, 143. 

relation to pore space, 143. 

relation to water, 144. 

usefulness of, 146. 
Alkali and irrigation, 120. 

control of, 121. 

effect of crops on, 119. 

movements of, 118. 

removal of, 120. 

tolerance of different plants to, 
119. 
Alkali soils, nature of, 118. 
Alluvial soils, character of, 23. 

described, 22. 

distribution of, 23. 

formation of, 22. 
Ammonia, absorption by plants, 156. 

test for, in soil, 141. 
Ammonification, 132. 
Animals, effect on structure, 41. 
Apatite, plant-food materials in, 7. 
Apparent specific gravity, and 
"heavy" soil, 38. 

and "light" soil, 38. 

of soil particles, 38. 
Auger for sampling soil, 29. 
Available plant-food materials, 94. 
Availability, conditions that in- 
fluence, 95. 

of nitrogenous fertilizers, 166. 

Bacteria, action on mineral matter, 

129. 
ammonification caused by, 132. 
conditions affecting growth, 128. 
decomposition of nitrogenous 

organic matter, 131. 
decomposition of non-nitrogenous 

organic matter, 130. 
examination of nodules for, 142. 



249 



250 



INDEX 



Bacteria, in relation to air supply, 128. 

in relation to lime, 189. 

in relation to moisture, 128. 

in relation to organic matter, 129. 

in relation to soil acidity, 129. 

in relation to soil fertility, 129. 

in relation to temperature, 129. 

nitrification caused by, 132. 

numbers in soils, 127. 
Basic slag, 172. 

Calcite, plant-food material in, 7. 
Capillary capacity, test for, 87. 
Capillary movement, test for, 86. 
Capillary water, 63. 
Carbon dioxide, conditions that affect 
quantity, 146. 

demonstration of formation in soil, 
154. 

demonstration of presence in soil, 
153. 

functions in soil, 147. 

percentage in bare and planted 
soil, 106. 

percentage in soil air, 145. 

production by microorganisms, 107. 

production in soils, 145. 
Chemical analysis of soil, 98. 
Chemical composition, of various 
soils, 91. 

relation to productiveness, 93. 
Class, the soil, defined, 33. 

in soil survey, 44. 

method for determination, 34. 
Classification of soils in survey, 43. 
Colluvial soils, described, 22. 

formation of, 22. 
Compaction of soil due to root 

growth, 2. 
Compost, building of a pile, 234. 
Crop rotation, 242. 
Crops, relation to soil texture, 32. 
Cumulose soils, composition of, 21. 

described, 20. 

formation of, 20. 
Cyanamid, changes in the soil, 162. 

composition of, 161. 

manufacture of, 161. 

Denitrification, 135. 

Dolomite, plant-food materials in, 7. 



Drainage, and length of growing 
season, 80. 

and available water, 79. 

benefits from, 78. 

by open ditches, 80. 

defined, 78. 

in relation to soil air, 79. 

in relation to tilth, 79. 
Drainage water, composition of, 

103, 104. 
Drains, arrangement of, 82. 

concrete, 81. 

tile, 81. 

Evaporation, prevention of, 74-77. 
proportion of rainfall lost by, 73. 

Feldspars, plant-food materials in, 7. 
Fertility of soil in relation to bac- 
teria, 129. 
Fertilizer constituents, trade values, 
200. 

experiments, plan for, 212. 

formulas for different crops, 210. 

ingredients, how to mix, 205. 

mixture, calculation of, 204. 
Fertilizers, brands of, 196. 

computation of wholesale value, 
202. 

conditions that influence effect of, 
217. 

consumption of, in U. S., 196. 

cumulative need of, 218. 
- effect on soil acidity, 114. 

for different crops, 207. 

for different soils, 211. 

for grasses, 208. 

for leguminous crops, 208. 

for orchards, 209. 

for root crops, 209. 

for small grains, 207. 

for vegetables, 209. 

high and low grade, 198. 

home mixing of, 203. 

inspection and control, 199. 

law of diminishing returns, 215. 

methods of applying, 214. 

nitrogenous, 155. 

nitrogenous, forms of nitrogen in, 
157. 

phosphoric acid, 171. 



INDEX 



251 



Fertilizers, phosphoric acid, tests for, 
177. 
potash, 179. 
potash, tests for, 185. 
response of soil to, 218. 
tests for nitrogenous fertilizers, 169. 
that should not be mixed, 203. 
the limiting factor, 215. 
the purchase and mixing of, 196. 
use. of, 207. 
Fertilizing the rotation, 213. 
Formation of soil, agencies concerned, 

11. 
Formations of soil, 18. 
Freezing and thawing of soil, effect 

on structure, 40. 
Frost, effect on rock disintegration, 
12. 

Gases, diffusion of, 144. 

effect on rock disintegration, 14. 
Germs, injurious to crops, 125. 

in soil, kinds of, 125. 

not directly injurious to crops, 126. 
Glacial soils, composition of, 26. 

described, 25. 

distribution of, 26. 

formation of, 25. 
Glaciers, effect on rock disintegra- 
tion, 13. 
Grains, fertilizers for, 207. 
Granite, losses during soil formation, 

15. 
Grasses, fertilizers for, 208. 
Gravitational water, 67. 
Green manures, crops used for, 238. 

effect on soil acidity, 115. 

handling, 240. 

materials supplied by, 236. 

nature of, 235. 

protective action of, 235. 

when to use, 235. 
Guano, 165. 
Gypsum, plant-food material in, 7. 

use on land, 192. 

Heat and cold, effect on rock disin- 
tegration, 12. 

Heat of soil, sources of, 149. 

"Heavy" soil, and absolute specific 
gravity, 35. 



"Heavy" soil, and apparent specific 

gravity, 38. 
Hematite, plant-food material in, 7. 
Hygroscopic water, 61. 

Ice, effect on rock disintegration, 13. 
Igneous rocks, 5. 

Inoculation of soil for legumes, 138. 
Iron, proportion in earth's crust, 4. 
Irrigation for removal of alkali, 120. 

Lacustrine soils, described, 25. 

formation of, 25. 
Law of diminishing returns, 215. 
Legumes, fertilizers for, 208. 
Leguminous plants as nitrogen fixers, 

137. 
"Light" soil, and absolute specific 
gravity, 35. 

and apparent specific gravity, 38. 
Lime, absorption by soils, 188. 

as a soil amendment, 187. 

caustic vs. ground limestone, 191. 

demonstration of flocculation by, 
194. 

effect on bacterial action, 189. 

effect on plant diseases, 190. 

effect on tilth, 189. 

fineness of grinding limestone, 191. 

forms of, 189. 

in relation to structure, 42. 

liberation of plant-food materials, 
190. 

magnesium, 190. 

proportion in earth's crust, 4. 

requirements of soils, 188. 

tests for, 193. 
Limestone, effect of fineness of grind- 
ing, 191. 

ground vs. caustic lime, 191. 

losses during soil formation, 15. 
Limiting factors in plant growth, 215. 
Loess, composition, 27. 

distribution, 26. 

Magnesia, proportion in earth's crust, 

4. 
Manure, cow, partial composition of, 

222. 
effect of food on composition of, 

224. 



252 



INDEX 



Manure, farm, 221. 

farm, agricultural evaluation of, 
226. 

farm, an unbalanced fertilizer, 223. 

farm, application to land, 231. 

farm, chemical composition of, 222. 

farm, commercial evaluation of, 
225. 

farm, covered barnyard for, 230. 

farm, deterioration of, 226. 

farm, experiments with, 233. 

farm, fermentations of, 227. 

farm, leaching of, 227. 

farm, methods of handling, 230. 

farm, place in crop rotation, 231. 

farm, protected more effective, 228. 

farm, reinforcing, 229. 

farm, solid and liquid, 221. 

green, crops used for, 238. 

green, materials supplied by, 236. 

green, handling, 240. 

green, nature of, 235. 

green, protective action, 235. 

green, when to use, 239. 

horse, partial composition of, 222. 

quantities voided by animals, 224. 

sheep, partial composition of, 222. 

swine, partial composition of, 222. 

value from different animals, 225. 
Marine soils, composition of, 24. 

described, 24. 

distribution of, 24. 

formation of, 24. 
Mechanical analysis of soil, 31. 

determination of class from, 34. 

method for, 46. 

of some typical soils, 32. 

relation of crops to, 32. 

size of separates, 32. 
Mechanical composition of various 

soil classes, 34. 
Metamorphic rocks, 5. 
Minerals, from which rocks are 
formed, 6. 

soil-forming, laboratory exercise, 8. 

plant-food materials in, 7. 

relation to soil, 6. 
Moisture, see water. 
Muck, origin, 21. 

relation to lime and potash, 22. 
Mulch, depths of, 75. 



Mulch, effectiveness of, 75. 

freqiiency of stirring, 74. 

of soil, nature and use, 74. 
Mulches, for moisture control, 74. 

test for conservation of water by, 
87. 

Nitrate formation, depths of occur- 
rence, 135. 

effect of aeration on, 132. 

effect of lime on, 189. 

effect of sod on, 134. 

effect of temperature on, 133. 
Nitrate of soda, effect on soils, 159. 

sources and composition, 157. 
Nitrates, as plant-food material, 156. 

crops markedly benefited by, 158. 

loss in drainage water, 135. 

test for, in soil, 140. 
Nitrification, 132. 

Nitrogen, animal products contain- 
ing, 163. 

availability in fertilizers, 166. 

effects on plant growth, 165. 

fixation, nature of, 136. 

fixation by free living germs, 139. 

fixation by plants, 137. 

forms in fertilizers, 157. 

forms in which used by plants, 156. 

in fertilizers, 155-170. 

in soils, quantities of different 
forms, 155. 

organic, direct utilization by 
plants, 156. 

organic, fertilizers containing, 162. 

vegetable products containing, 163. 
Nodules, examination for, 142. 

on leguminous plants, 137. 

Orchards, fertilizers for, 209. 
Organic matter, and drainage, 53. 

and formation of acids, 55. 

and nitrogen, 54. 

and plant-food material, 54. 

and soil color, 53. 

and soil organisms, 54. 

benefits of, 52. 

effect on structure, 41. 

effect on availability of plant nu- 
trients, 102. 

estimation of, 58. 



INDEX 



253 



Organic matter, examination of soil 
for, 58. 

extraction of, 59. 

influence on rate of percolation, 59. 

influence on water held by soils, 60. 

injurious effect, 55. 

in soil, description, 51. 

in soil management, 55. 

kinds of, 51. 

porosity of, 53. 

sources of, 57. 
Oxygen, proportion in earth's crust, 4. 

Packing, subsurface, 78. 
Particles of soil, examination, 46. 

number per gram, 30. 

relative sizes, 31. 

shape of, 30. 

space occupied by, 30. 
Peat, origin, 21. 
Percolation, test for rate of, 86. 
Plant constituents, obtained from air 
or water, 3. 

obtained from soil, 3. 
Plant-food materials, available and 
unavailable, 94. 

essential to growth, 3. 

absorption by plants, 105. 

in apatite, 7. 

in calcite, 7. 

in drainage water, 102. 

in dolomite, 7. 

in farm manure, 222. 

in green manures, 236. 

in gypsum, 7. 

in hematite, 7. 

in liquid excreta, 222. 

in minerals, 7. 

in soils, 90. 

in solid excreta, 222. 

laboratory exercise, 9. 

liberation by lime, 190. 

movement of, 93. 

obtained from air or water, 3. 

obtained from soil, 3. 

possible exhaustion, 109. 

proportion in soils, 93. 

quantities in earth's crust, 4. 

removed by crops, 108. 

total supply in soils, 92. 

variations in soils, 90. 



Plant growth, conditions of, labora- 
tory exercise, 9. 
Plant nutrients, laboratory exercise, 

9. 
Plant roots, aid in solution of soil 
constituents, 106. 
solvent action, 107. 
Plants, effect on rock disintegration, 
14. 
substances essential to growth, 3. 
uses of water by, 2. 
Phosphate, bone, 171. 

mineral, 171. 
Phosphoric acid, effect on plant 

growth, 175. 
Phosphoric acid, plants benefited by, 
176. 
proportion in earth's crust, 4. 
reverted, 173. 
Phosphoric acid fertilizers, 171. 

availability of, 174. 
Pore space, its determination, 49. 

relation to structure, 37. 
Potash, effect on plant growth, 181. 

proportion in earth's crust, 4. 
Potash fertilizers, sources, 179. 

wood ashes, 180. 
Province, the soil, in soil survey, 44. 

Quartz, substance of which composed, 

7. 

Residual soils, composition, 20. 
described, 18. 
distribution of, 20. 
loss during formation, 19. 
Rock, changes in soil formation, 15. 
disintegration by heat and cold, 12. 
disintegration, effect of gases on, 

14. 
disintegration, effect of glaciers on, 

13. 
disintegration, effect of ice on, 13. 
disintegration, effect of plants on, 

14. 
erosion by wind, 14. 
expansion by heat, 12. 
relation to soil, 15. 
Rocks, from which soil has been 
formed, 5. 
igneous, 5. 



254 



INDEX 



Rocks, losses during soil formation, 15. 

metamorphic, 5. 

sedimentary, 5. 

soil-forming, laboratory exercise, 9. 
Rolling land, 78. 
Root crops, fertilizers for, 209. 
Root systems of different crops, 243. 
Roots of plants, effect on structure, 

41. 
Rotation of crops, 242. 

and soil productiveness, 242. 

management of, 246. 

nutrients removed by, 243. 

Sedentary soil, 18. 
Sedimentary rocks, 5. 
Separates of soil, 32. 

chemical composition of, 36. 
examination, 46. 
properties of, 35. 
Series, the soil, in soil survey, 44. 
Soil, as a mechanical support for 
plants, 1. 
as a reservoir for water, 2. 
as a source of plant-food material, 

2. 
changes during formation from 
rock, 15. 
Soil class, in classification for surveys, 
44. 
method for its determination, 47. 
Soil formation, agencies concerned, 
11. 
and transportation, laboratory 
exercise, 17. 
Soil formations, 1, 18. 
Soil-forming minerals, laboratory 

exercise, 8. 
Soil-forming rocks, laboratory exer- 
cise, 9. 
Soil mulch, nature and use, 74. 
Soil province, in classification for 

surveys, 44. 
Soil, relation to rock, 15. 
Soil series, in classification for sur- 
veys, 44. 
Soil survey, described, 43. 
classification of soil for, 43. 
information furnished by, 44. 
Soil type, in classification for surveys, 
44. 



Soils, residual, 18. 

sedentary, 18. 

transported, 18. 
Specific gravity, apparent, its deter- 
mination, 48. 

of soil, apparent, 38. 

of soil particles, absolute, 35. 

of soil particles, apparent, 38. 
Structure, of soil, as affected by freez- 
ing and thawing, 40. 

as affected by lime, 42. 

as affected by organic matter, 41. 

as affected by plant roots and 
animals, 41. 

as affected by tillage, 42. 

as affected by wetting and drying, 
40. 

conditions that affect, 39. 

granular or crumbly, 37. 

defined, 37. 

relation to pore space, 37. 

relation to texture, 39. 

relation to tilth, 39. 

operations that affect, 39. 

separate grain, 37. 
Subsurface packing, 78. 
Sulfate of ammonia, action when 
applied to soils, 160. 

composition, 160. 

sources, 159. 
Sulfur, as a fertilizer, 182. 

contained in crops, 182. 

contained in drainage water, 183. 

contained in fertilizers, 184. 

contained in soils, 183. 

proportion in earth's crust, 4. 

Temperature, control of, 151. 

demonstration of effect of slope on, 
154. 

factors that modify, 150. 

of soil and atmosphere, 149. 

of soils, relation to plant growth, 
148. 
Texture, of soil, described, 30. 

relation to crops, 32. 

relation to structure, 39. 
Tile, concrete, 81. 

drains, 81. 

laying, 83. 
Tillage in relation to structure, 42. 



INDEX 



255 



Tilth, as affected by lime, 189. 

in relation to drainage, 79. 

relation to structure, 39. 
Toxic substances and crop rotation, 

246. 
Transpiration, as affected by soil 
moisture, 69. 

by different crops, 69. 

conditions affecting, 70. 

ratio, 69. 

relation to soil fertility, 70. 

test for loss by, 88. 
Transported soil, 18. 
Type, the soil, in soil survey, 44. 

Vegetables, fertilizers for, 209. 

Water, as a soil transporting agent, 
13. 

capillary, capacity of soils, 63. 

capillary, definition, 62. 

capillary, effect of structure on 
movement of, 65. 

capillary, effect of texture on 
movement of, 65. 

capillary, height of column and 
movement, 66. 

capillary movement and plant re- 
quirement, 71. 

capillary, movement of, 64. 

capillary, properties of, 63. 

carrying power for rock debris, 13. 

control of soil content, 72. 

effect on rock disintegration, 12. 

evaporation from soil, 73. 



Water, expansive power in freezing, 
12. 

forms in soils, 61. 

gravitational, definition, 62. 

gravitational, movement, 67. 

gravitational, properties of, 66. 

hygroscopic, definition, 61. 

hygroscopic, properties of, 62. 

in soil, determination of per cent, 
85. 

optimum content for plant growth, 
71. 

percolation through soil, 73. 

quantity required to mature a crop, 
70. 

relation to plants, 67. 

requirements of plants, 68. 

run-off, 72. 

solvent action on rock, 12. 

test for capacity of soil for, 87. 

test for capillary movement, 86. 

test for conservation by mulch, 87. 

test for loss by transpiration, 88. 

test for rate of percolation, 86. 

uses by plants, 2. 

ways in which useful to plants, 68. 
Water-soluble matter in soil, 96. 

test for, 111. 
Water table, 67. 

Weeds that flourish on acid soils, 115. 
Wetting and drying soil, affect on 

structure, 40. 
Wind, action in transporting soil, 14. 

erosive action on rocks, 14. 
Windbreaks, to decrease evaporation. 
78. • 



Printed in the United States of America. 



